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Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 4625 |
1 files changed, 4625 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c new file mode 100644 index 000000000000..61d1a83aabf5 --- /dev/null +++ b/kernel/rcu/tree.c @@ -0,0 +1,4625 @@ +/* + * Read-Copy Update mechanism for mutual exclusion + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. + * + * Copyright IBM Corporation, 2008 + * + * Authors: Dipankar Sarma <dipankar@in.ibm.com> + * Manfred Spraul <manfred@colorfullife.com> + * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version + * + * Based on the original work by Paul McKenney <paulmck@us.ibm.com> + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. + * + * For detailed explanation of Read-Copy Update mechanism see - + * Documentation/RCU + */ +#include <linux/types.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/spinlock.h> +#include <linux/smp.h> +#include <linux/rcupdate.h> +#include <linux/interrupt.h> +#include <linux/sched.h> +#include <linux/nmi.h> +#include <linux/atomic.h> +#include <linux/bitops.h> +#include <linux/export.h> +#include <linux/completion.h> +#include <linux/moduleparam.h> +#include <linux/module.h> +#include <linux/percpu.h> +#include <linux/notifier.h> +#include <linux/cpu.h> +#include <linux/mutex.h> +#include <linux/time.h> +#include <linux/kernel_stat.h> +#include <linux/wait.h> +#include <linux/kthread.h> +#include <linux/prefetch.h> +#include <linux/delay.h> +#include <linux/stop_machine.h> +#include <linux/random.h> +#include <linux/trace_events.h> +#include <linux/suspend.h> + +#include <soc/qcom/watchdog.h> + +#include "tree.h" +#include "rcu.h" + +MODULE_ALIAS("rcutree"); +#ifdef MODULE_PARAM_PREFIX +#undef MODULE_PARAM_PREFIX +#endif +#define MODULE_PARAM_PREFIX "rcutree." + +/* Data structures. */ + +static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; +static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; +static struct lock_class_key rcu_exp_class[RCU_NUM_LVLS]; + +/* + * In order to export the rcu_state name to the tracing tools, it + * needs to be added in the __tracepoint_string section. + * This requires defining a separate variable tp_<sname>_varname + * that points to the string being used, and this will allow + * the tracing userspace tools to be able to decipher the string + * address to the matching string. + */ +#ifdef CONFIG_TRACING +# define DEFINE_RCU_TPS(sname) \ +static char sname##_varname[] = #sname; \ +static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; +# define RCU_STATE_NAME(sname) sname##_varname +#else +# define DEFINE_RCU_TPS(sname) +# define RCU_STATE_NAME(sname) __stringify(sname) +#endif + +#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \ +DEFINE_RCU_TPS(sname) \ +static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \ +struct rcu_state sname##_state = { \ + .level = { &sname##_state.node[0] }, \ + .rda = &sname##_data, \ + .call = cr, \ + .gp_state = RCU_GP_IDLE, \ + .gpnum = 0UL - 300UL, \ + .completed = 0UL - 300UL, \ + .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \ + .orphan_nxttail = &sname##_state.orphan_nxtlist, \ + .orphan_donetail = &sname##_state.orphan_donelist, \ + .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ + .name = RCU_STATE_NAME(sname), \ + .abbr = sabbr, \ +} + +RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); +RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh); + +static struct rcu_state *const rcu_state_p; +static struct rcu_data __percpu *const rcu_data_p; +LIST_HEAD(rcu_struct_flavors); + +/* Dump rcu_node combining tree at boot to verify correct setup. */ +static bool dump_tree; +module_param(dump_tree, bool, 0444); +/* Control rcu_node-tree auto-balancing at boot time. */ +static bool rcu_fanout_exact; +module_param(rcu_fanout_exact, bool, 0444); +/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */ +static int rcu_fanout_leaf = RCU_FANOUT_LEAF; +module_param(rcu_fanout_leaf, int, 0444); +int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; +/* Number of rcu_nodes at specified level. */ +static int num_rcu_lvl[] = NUM_RCU_LVL_INIT; +int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ + +/* + * The rcu_scheduler_active variable transitions from zero to one just + * before the first task is spawned. So when this variable is zero, RCU + * can assume that there is but one task, allowing RCU to (for example) + * optimize synchronize_sched() to a simple barrier(). When this variable + * is one, RCU must actually do all the hard work required to detect real + * grace periods. This variable is also used to suppress boot-time false + * positives from lockdep-RCU error checking. + */ +int rcu_scheduler_active __read_mostly; +EXPORT_SYMBOL_GPL(rcu_scheduler_active); + +/* + * The rcu_scheduler_fully_active variable transitions from zero to one + * during the early_initcall() processing, which is after the scheduler + * is capable of creating new tasks. So RCU processing (for example, + * creating tasks for RCU priority boosting) must be delayed until after + * rcu_scheduler_fully_active transitions from zero to one. We also + * currently delay invocation of any RCU callbacks until after this point. + * + * It might later prove better for people registering RCU callbacks during + * early boot to take responsibility for these callbacks, but one step at + * a time. + */ +static int rcu_scheduler_fully_active __read_mostly; + +static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); +static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); +static void invoke_rcu_core(void); +static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); +static void rcu_report_exp_rdp(struct rcu_state *rsp, + struct rcu_data *rdp, bool wake); + +/* rcuc/rcub kthread realtime priority */ +#ifdef CONFIG_RCU_KTHREAD_PRIO +static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO; +#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */ +static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; +#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */ +module_param(kthread_prio, int, 0644); + +/* Delay in jiffies for grace-period initialization delays, debug only. */ + +#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT +static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY; +module_param(gp_preinit_delay, int, 0644); +#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */ +static const int gp_preinit_delay; +#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */ + +#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT +static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY; +module_param(gp_init_delay, int, 0644); +#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ +static const int gp_init_delay; +#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ + +#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP +static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY; +module_param(gp_cleanup_delay, int, 0644); +#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */ +static const int gp_cleanup_delay; +#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */ + +/* + * Number of grace periods between delays, normalized by the duration of + * the delay. The longer the the delay, the more the grace periods between + * each delay. The reason for this normalization is that it means that, + * for non-zero delays, the overall slowdown of grace periods is constant + * regardless of the duration of the delay. This arrangement balances + * the need for long delays to increase some race probabilities with the + * need for fast grace periods to increase other race probabilities. + */ +#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */ + +/* + * Track the rcutorture test sequence number and the update version + * number within a given test. The rcutorture_testseq is incremented + * on every rcutorture module load and unload, so has an odd value + * when a test is running. The rcutorture_vernum is set to zero + * when rcutorture starts and is incremented on each rcutorture update. + * These variables enable correlating rcutorture output with the + * RCU tracing information. + */ +unsigned long rcutorture_testseq; +unsigned long rcutorture_vernum; + +/* + * Compute the mask of online CPUs for the specified rcu_node structure. + * This will not be stable unless the rcu_node structure's ->lock is + * held, but the bit corresponding to the current CPU will be stable + * in most contexts. + */ +unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) +{ + return READ_ONCE(rnp->qsmaskinitnext); +} + +/* + * Return true if an RCU grace period is in progress. The READ_ONCE()s + * permit this function to be invoked without holding the root rcu_node + * structure's ->lock, but of course results can be subject to change. + */ +static int rcu_gp_in_progress(struct rcu_state *rsp) +{ + return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum); +} + +/* + * Note a quiescent state. Because we do not need to know + * how many quiescent states passed, just if there was at least + * one since the start of the grace period, this just sets a flag. + * The caller must have disabled preemption. + */ +void rcu_sched_qs(void) +{ + if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s)) + return; + trace_rcu_grace_period(TPS("rcu_sched"), + __this_cpu_read(rcu_sched_data.gpnum), + TPS("cpuqs")); + __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false); + if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) + return; + __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false); + rcu_report_exp_rdp(&rcu_sched_state, + this_cpu_ptr(&rcu_sched_data), true); +} + +void rcu_bh_qs(void) +{ + if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) { + trace_rcu_grace_period(TPS("rcu_bh"), + __this_cpu_read(rcu_bh_data.gpnum), + TPS("cpuqs")); + __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false); + } +} + +static DEFINE_PER_CPU(int, rcu_sched_qs_mask); + +static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { + .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, + .dynticks = ATOMIC_INIT(1), +#ifdef CONFIG_NO_HZ_FULL_SYSIDLE + .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE, + .dynticks_idle = ATOMIC_INIT(1), +#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ +}; + +DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr); +EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); + +/* + * Let the RCU core know that this CPU has gone through the scheduler, + * which is a quiescent state. This is called when the need for a + * quiescent state is urgent, so we burn an atomic operation and full + * memory barriers to let the RCU core know about it, regardless of what + * this CPU might (or might not) do in the near future. + * + * We inform the RCU core by emulating a zero-duration dyntick-idle + * period, which we in turn do by incrementing the ->dynticks counter + * by two. + * + * The caller must have disabled interrupts. + */ +static void rcu_momentary_dyntick_idle(void) +{ + struct rcu_data *rdp; + struct rcu_dynticks *rdtp; + int resched_mask; + struct rcu_state *rsp; + + /* + * Yes, we can lose flag-setting operations. This is OK, because + * the flag will be set again after some delay. + */ + resched_mask = raw_cpu_read(rcu_sched_qs_mask); + raw_cpu_write(rcu_sched_qs_mask, 0); + + /* Find the flavor that needs a quiescent state. */ + for_each_rcu_flavor(rsp) { + rdp = raw_cpu_ptr(rsp->rda); + if (!(resched_mask & rsp->flavor_mask)) + continue; + smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */ + if (READ_ONCE(rdp->mynode->completed) != + READ_ONCE(rdp->cond_resched_completed)) + continue; + + /* + * Pretend to be momentarily idle for the quiescent state. + * This allows the grace-period kthread to record the + * quiescent state, with no need for this CPU to do anything + * further. + */ + rdtp = this_cpu_ptr(&rcu_dynticks); + smp_mb__before_atomic(); /* Earlier stuff before QS. */ + atomic_add(2, &rdtp->dynticks); /* QS. */ + smp_mb__after_atomic(); /* Later stuff after QS. */ + break; + } +} + +/* + * Note a context switch. This is a quiescent state for RCU-sched, + * and requires special handling for preemptible RCU. + * The caller must have disabled interrupts. + */ +void rcu_note_context_switch(void) +{ + barrier(); /* Avoid RCU read-side critical sections leaking down. */ + trace_rcu_utilization(TPS("Start context switch")); + rcu_sched_qs(); + rcu_preempt_note_context_switch(); + if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) + rcu_momentary_dyntick_idle(); + trace_rcu_utilization(TPS("End context switch")); + barrier(); /* Avoid RCU read-side critical sections leaking up. */ +} +EXPORT_SYMBOL_GPL(rcu_note_context_switch); + +/* + * Register a quiescent state for all RCU flavors. If there is an + * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight + * dyntick-idle quiescent state visible to other CPUs (but only for those + * RCU flavors in desperate need of a quiescent state, which will normally + * be none of them). Either way, do a lightweight quiescent state for + * all RCU flavors. + * + * The barrier() calls are redundant in the common case when this is + * called externally, but just in case this is called from within this + * file. + * + */ +void rcu_all_qs(void) +{ + unsigned long flags; + + barrier(); /* Avoid RCU read-side critical sections leaking down. */ + if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) { + local_irq_save(flags); + rcu_momentary_dyntick_idle(); + local_irq_restore(flags); + } + this_cpu_inc(rcu_qs_ctr); + barrier(); /* Avoid RCU read-side critical sections leaking up. */ +} +EXPORT_SYMBOL_GPL(rcu_all_qs); + +static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */ +static long qhimark = 10000; /* If this many pending, ignore blimit. */ +static long qlowmark = 100; /* Once only this many pending, use blimit. */ + +module_param(blimit, long, 0444); +module_param(qhimark, long, 0444); +module_param(qlowmark, long, 0444); + +static ulong jiffies_till_first_fqs = ULONG_MAX; +static ulong jiffies_till_next_fqs = ULONG_MAX; + +module_param(jiffies_till_first_fqs, ulong, 0644); +module_param(jiffies_till_next_fqs, ulong, 0644); + +/* + * How long the grace period must be before we start recruiting + * quiescent-state help from rcu_note_context_switch(). + */ +static ulong jiffies_till_sched_qs = HZ / 20; +module_param(jiffies_till_sched_qs, ulong, 0644); + +static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp); +static void force_qs_rnp(struct rcu_state *rsp, + int (*f)(struct rcu_data *rsp, bool *isidle, + unsigned long *maxj), + bool *isidle, unsigned long *maxj); +static void force_quiescent_state(struct rcu_state *rsp); +static int rcu_pending(void); + +/* + * Return the number of RCU batches started thus far for debug & stats. + */ +unsigned long rcu_batches_started(void) +{ + return rcu_state_p->gpnum; +} +EXPORT_SYMBOL_GPL(rcu_batches_started); + +/* + * Return the number of RCU-sched batches started thus far for debug & stats. + */ +unsigned long rcu_batches_started_sched(void) +{ + return rcu_sched_state.gpnum; +} +EXPORT_SYMBOL_GPL(rcu_batches_started_sched); + +/* + * Return the number of RCU BH batches started thus far for debug & stats. + */ +unsigned long rcu_batches_started_bh(void) +{ + return rcu_bh_state.gpnum; +} +EXPORT_SYMBOL_GPL(rcu_batches_started_bh); + +/* + * Return the number of RCU batches completed thus far for debug & stats. + */ +unsigned long rcu_batches_completed(void) +{ + return rcu_state_p->completed; +} +EXPORT_SYMBOL_GPL(rcu_batches_completed); + +/* + * Return the number of RCU-sched batches completed thus far for debug & stats. + */ +unsigned long rcu_batches_completed_sched(void) +{ + return rcu_sched_state.completed; +} +EXPORT_SYMBOL_GPL(rcu_batches_completed_sched); + +/* + * Return the number of RCU BH batches completed thus far for debug & stats. + */ +unsigned long rcu_batches_completed_bh(void) +{ + return rcu_bh_state.completed; +} +EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); + +/* + * Force a quiescent state. + */ +void rcu_force_quiescent_state(void) +{ + force_quiescent_state(rcu_state_p); +} +EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); + +/* + * Force a quiescent state for RCU BH. + */ +void rcu_bh_force_quiescent_state(void) +{ + force_quiescent_state(&rcu_bh_state); +} +EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); + +/* + * Force a quiescent state for RCU-sched. + */ +void rcu_sched_force_quiescent_state(void) +{ + force_quiescent_state(&rcu_sched_state); +} +EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); + +/* + * Show the state of the grace-period kthreads. + */ +void show_rcu_gp_kthreads(void) +{ + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) { + pr_info("%s: wait state: %d ->state: %#lx\n", + rsp->name, rsp->gp_state, rsp->gp_kthread->state); + /* sched_show_task(rsp->gp_kthread); */ + } +} +EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); + +/* + * Record the number of times rcutorture tests have been initiated and + * terminated. This information allows the debugfs tracing stats to be + * correlated to the rcutorture messages, even when the rcutorture module + * is being repeatedly loaded and unloaded. In other words, we cannot + * store this state in rcutorture itself. + */ +void rcutorture_record_test_transition(void) +{ + rcutorture_testseq++; + rcutorture_vernum = 0; +} +EXPORT_SYMBOL_GPL(rcutorture_record_test_transition); + +/* + * Send along grace-period-related data for rcutorture diagnostics. + */ +void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, + unsigned long *gpnum, unsigned long *completed) +{ + struct rcu_state *rsp = NULL; + + switch (test_type) { + case RCU_FLAVOR: + rsp = rcu_state_p; + break; + case RCU_BH_FLAVOR: + rsp = &rcu_bh_state; + break; + case RCU_SCHED_FLAVOR: + rsp = &rcu_sched_state; + break; + default: + break; + } + if (rsp != NULL) { + *flags = READ_ONCE(rsp->gp_flags); + *gpnum = READ_ONCE(rsp->gpnum); + *completed = READ_ONCE(rsp->completed); + return; + } + *flags = 0; + *gpnum = 0; + *completed = 0; +} +EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); + +/* + * Record the number of writer passes through the current rcutorture test. + * This is also used to correlate debugfs tracing stats with the rcutorture + * messages. + */ +void rcutorture_record_progress(unsigned long vernum) +{ + rcutorture_vernum++; +} +EXPORT_SYMBOL_GPL(rcutorture_record_progress); + +/* + * Does the CPU have callbacks ready to be invoked? + */ +static int +cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) +{ + return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] && + rdp->nxttail[RCU_DONE_TAIL] != NULL; +} + +/* + * Return the root node of the specified rcu_state structure. + */ +static struct rcu_node *rcu_get_root(struct rcu_state *rsp) +{ + return &rsp->node[0]; +} + +/* + * Is there any need for future grace periods? + * Interrupts must be disabled. If the caller does not hold the root + * rnp_node structure's ->lock, the results are advisory only. + */ +static int rcu_future_needs_gp(struct rcu_state *rsp) +{ + struct rcu_node *rnp = rcu_get_root(rsp); + int idx = (READ_ONCE(rnp->completed) + 1) & 0x1; + int *fp = &rnp->need_future_gp[idx]; + + return READ_ONCE(*fp); +} + +/* + * Does the current CPU require a not-yet-started grace period? + * The caller must have disabled interrupts to prevent races with + * normal callback registry. + */ +static int +cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) +{ + int i; + + if (rcu_gp_in_progress(rsp)) + return 0; /* No, a grace period is already in progress. */ + if (rcu_future_needs_gp(rsp)) + return 1; /* Yes, a no-CBs CPU needs one. */ + if (!rdp->nxttail[RCU_NEXT_TAIL]) + return 0; /* No, this is a no-CBs (or offline) CPU. */ + if (*rdp->nxttail[RCU_NEXT_READY_TAIL]) + return 1; /* Yes, this CPU has newly registered callbacks. */ + for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) + if (rdp->nxttail[i - 1] != rdp->nxttail[i] && + ULONG_CMP_LT(READ_ONCE(rsp->completed), + rdp->nxtcompleted[i])) + return 1; /* Yes, CBs for future grace period. */ + return 0; /* No grace period needed. */ +} + +/* + * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state + * + * If the new value of the ->dynticks_nesting counter now is zero, + * we really have entered idle, and must do the appropriate accounting. + * The caller must have disabled interrupts. + */ +static void rcu_eqs_enter_common(long long oldval, bool user) +{ + struct rcu_state *rsp; + struct rcu_data *rdp; + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting); + if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + !user && !is_idle_task(current)) { + struct task_struct *idle __maybe_unused = + idle_task(smp_processor_id()); + + trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0); + ftrace_dump(DUMP_ORIG); + WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", + current->pid, current->comm, + idle->pid, idle->comm); /* must be idle task! */ + } + for_each_rcu_flavor(rsp) { + rdp = this_cpu_ptr(rsp->rda); + do_nocb_deferred_wakeup(rdp); + } + rcu_prepare_for_idle(); + /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ + smp_mb__before_atomic(); /* See above. */ + atomic_inc(&rdtp->dynticks); + smp_mb__after_atomic(); /* Force ordering with next sojourn. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + atomic_read(&rdtp->dynticks) & 0x1); + rcu_dynticks_task_enter(); + + /* + * It is illegal to enter an extended quiescent state while + * in an RCU read-side critical section. + */ + RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), + "Illegal idle entry in RCU read-side critical section."); + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), + "Illegal idle entry in RCU-bh read-side critical section."); + RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), + "Illegal idle entry in RCU-sched read-side critical section."); +} + +/* + * Enter an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. + */ +static void rcu_eqs_enter(bool user) +{ + long long oldval; + struct rcu_dynticks *rdtp; + + rdtp = this_cpu_ptr(&rcu_dynticks); + oldval = rdtp->dynticks_nesting; + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + (oldval & DYNTICK_TASK_NEST_MASK) == 0); + if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) { + rdtp->dynticks_nesting = 0; + rcu_eqs_enter_common(oldval, user); + } else { + rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; + } +} + +/** + * rcu_idle_enter - inform RCU that current CPU is entering idle + * + * Enter idle mode, in other words, -leave- the mode in which RCU + * read-side critical sections can occur. (Though RCU read-side + * critical sections can occur in irq handlers in idle, a possibility + * handled by irq_enter() and irq_exit().) + * + * We crowbar the ->dynticks_nesting field to zero to allow for + * the possibility of usermode upcalls having messed up our count + * of interrupt nesting level during the prior busy period. + */ +void rcu_idle_enter(void) +{ + unsigned long flags; + + local_irq_save(flags); + rcu_eqs_enter(false); + rcu_sysidle_enter(0); + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(rcu_idle_enter); + +#ifdef CONFIG_NO_HZ_FULL +/** + * rcu_user_enter - inform RCU that we are resuming userspace. + * + * Enter RCU idle mode right before resuming userspace. No use of RCU + * is permitted between this call and rcu_user_exit(). This way the + * CPU doesn't need to maintain the tick for RCU maintenance purposes + * when the CPU runs in userspace. + */ +void rcu_user_enter(void) +{ + rcu_eqs_enter(1); +} +#endif /* CONFIG_NO_HZ_FULL */ + +/** + * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle + * + * Exit from an interrupt handler, which might possibly result in entering + * idle mode, in other words, leaving the mode in which read-side critical + * sections can occur. + * + * This code assumes that the idle loop never does anything that might + * result in unbalanced calls to irq_enter() and irq_exit(). If your + * architecture violates this assumption, RCU will give you what you + * deserve, good and hard. But very infrequently and irreproducibly. + * + * Use things like work queues to work around this limitation. + * + * You have been warned. + */ +void rcu_irq_exit(void) +{ + unsigned long flags; + long long oldval; + struct rcu_dynticks *rdtp; + + local_irq_save(flags); + rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + + RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!"); + oldval = rdtp->dynticks_nesting; + rdtp->dynticks_nesting--; + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + rdtp->dynticks_nesting < 0); + if (rdtp->dynticks_nesting) + trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting); + else + rcu_eqs_enter_common(oldval, true); + rcu_sysidle_enter(1); + local_irq_restore(flags); +} + +/* + * rcu_eqs_exit_common - current CPU moving away from extended quiescent state + * + * If the new value of the ->dynticks_nesting counter was previously zero, + * we really have exited idle, and must do the appropriate accounting. + * The caller must have disabled interrupts. + */ +static void rcu_eqs_exit_common(long long oldval, int user) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + rcu_dynticks_task_exit(); + smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */ + atomic_inc(&rdtp->dynticks); + /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ + smp_mb__after_atomic(); /* See above. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + !(atomic_read(&rdtp->dynticks) & 0x1)); + rcu_cleanup_after_idle(); + trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting); + if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + !user && !is_idle_task(current)) { + struct task_struct *idle __maybe_unused = + idle_task(smp_processor_id()); + + trace_rcu_dyntick(TPS("Error on exit: not idle task"), + oldval, rdtp->dynticks_nesting); + ftrace_dump(DUMP_ORIG); + WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", + current->pid, current->comm, + idle->pid, idle->comm); /* must be idle task! */ + } +} + +/* + * Exit an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. + */ +static void rcu_eqs_exit(bool user) +{ + struct rcu_dynticks *rdtp; + long long oldval; + + rdtp = this_cpu_ptr(&rcu_dynticks); + oldval = rdtp->dynticks_nesting; + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); + if (oldval & DYNTICK_TASK_NEST_MASK) { + rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; + } else { + rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; + rcu_eqs_exit_common(oldval, user); + } +} + +/** + * rcu_idle_exit - inform RCU that current CPU is leaving idle + * + * Exit idle mode, in other words, -enter- the mode in which RCU + * read-side critical sections can occur. + * + * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to + * allow for the possibility of usermode upcalls messing up our count + * of interrupt nesting level during the busy period that is just + * now starting. + */ +void rcu_idle_exit(void) +{ + unsigned long flags; + + local_irq_save(flags); + rcu_eqs_exit(false); + rcu_sysidle_exit(0); + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(rcu_idle_exit); + +#ifdef CONFIG_NO_HZ_FULL +/** + * rcu_user_exit - inform RCU that we are exiting userspace. + * + * Exit RCU idle mode while entering the kernel because it can + * run a RCU read side critical section anytime. + */ +void rcu_user_exit(void) +{ + rcu_eqs_exit(1); +} +#endif /* CONFIG_NO_HZ_FULL */ + +/** + * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle + * + * Enter an interrupt handler, which might possibly result in exiting + * idle mode, in other words, entering the mode in which read-side critical + * sections can occur. + * + * Note that the Linux kernel is fully capable of entering an interrupt + * handler that it never exits, for example when doing upcalls to + * user mode! This code assumes that the idle loop never does upcalls to + * user mode. If your architecture does do upcalls from the idle loop (or + * does anything else that results in unbalanced calls to the irq_enter() + * and irq_exit() functions), RCU will give you what you deserve, good + * and hard. But very infrequently and irreproducibly. + * + * Use things like work queues to work around this limitation. + * + * You have been warned. + */ +void rcu_irq_enter(void) +{ + unsigned long flags; + struct rcu_dynticks *rdtp; + long long oldval; + + local_irq_save(flags); + rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + + RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!"); + oldval = rdtp->dynticks_nesting; + rdtp->dynticks_nesting++; + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + rdtp->dynticks_nesting == 0); + if (oldval) + trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting); + else + rcu_eqs_exit_common(oldval, true); + rcu_sysidle_exit(1); + local_irq_restore(flags); +} + +/** + * rcu_nmi_enter - inform RCU of entry to NMI context + * + * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and + * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know + * that the CPU is active. This implementation permits nested NMIs, as + * long as the nesting level does not overflow an int. (You will probably + * run out of stack space first.) + */ +void rcu_nmi_enter(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + int incby = 2; + + /* Complain about underflow. */ + WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0); + + /* + * If idle from RCU viewpoint, atomically increment ->dynticks + * to mark non-idle and increment ->dynticks_nmi_nesting by one. + * Otherwise, increment ->dynticks_nmi_nesting by two. This means + * if ->dynticks_nmi_nesting is equal to one, we are guaranteed + * to be in the outermost NMI handler that interrupted an RCU-idle + * period (observation due to Andy Lutomirski). + */ + if (!(atomic_read(&rdtp->dynticks) & 0x1)) { + smp_mb__before_atomic(); /* Force delay from prior write. */ + atomic_inc(&rdtp->dynticks); + /* atomic_inc() before later RCU read-side crit sects */ + smp_mb__after_atomic(); /* See above. */ + WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); + incby = 1; + } + rdtp->dynticks_nmi_nesting += incby; + barrier(); +} + +/** + * rcu_nmi_exit - inform RCU of exit from NMI context + * + * If we are returning from the outermost NMI handler that interrupted an + * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting + * to let the RCU grace-period handling know that the CPU is back to + * being RCU-idle. + */ +void rcu_nmi_exit(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + /* + * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. + * (We are exiting an NMI handler, so RCU better be paying attention + * to us!) + */ + WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0); + WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); + + /* + * If the nesting level is not 1, the CPU wasn't RCU-idle, so + * leave it in non-RCU-idle state. + */ + if (rdtp->dynticks_nmi_nesting != 1) { + rdtp->dynticks_nmi_nesting -= 2; + return; + } + + /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ + rdtp->dynticks_nmi_nesting = 0; + /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ + smp_mb__before_atomic(); /* See above. */ + atomic_inc(&rdtp->dynticks); + smp_mb__after_atomic(); /* Force delay to next write. */ + WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); +} + +/** + * __rcu_is_watching - are RCU read-side critical sections safe? + * + * Return true if RCU is watching the running CPU, which means that + * this CPU can safely enter RCU read-side critical sections. Unlike + * rcu_is_watching(), the caller of __rcu_is_watching() must have at + * least disabled preemption. + */ +bool notrace __rcu_is_watching(void) +{ + return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1; +} + +/** + * rcu_is_watching - see if RCU thinks that the current CPU is idle + * + * If the current CPU is in its idle loop and is neither in an interrupt + * or NMI handler, return true. + */ +bool notrace rcu_is_watching(void) +{ + bool ret; + + preempt_disable_notrace(); + ret = __rcu_is_watching(); + preempt_enable_notrace(); + return ret; +} +EXPORT_SYMBOL_GPL(rcu_is_watching); + +#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) + +/* + * Is the current CPU online? Disable preemption to avoid false positives + * that could otherwise happen due to the current CPU number being sampled, + * this task being preempted, its old CPU being taken offline, resuming + * on some other CPU, then determining that its old CPU is now offline. + * It is OK to use RCU on an offline processor during initial boot, hence + * the check for rcu_scheduler_fully_active. Note also that it is OK + * for a CPU coming online to use RCU for one jiffy prior to marking itself + * online in the cpu_online_mask. Similarly, it is OK for a CPU going + * offline to continue to use RCU for one jiffy after marking itself + * offline in the cpu_online_mask. This leniency is necessary given the + * non-atomic nature of the online and offline processing, for example, + * the fact that a CPU enters the scheduler after completing the CPU_DYING + * notifiers. + * + * This is also why RCU internally marks CPUs online during the + * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase. + * + * Disable checking if in an NMI handler because we cannot safely report + * errors from NMI handlers anyway. + */ +bool rcu_lockdep_current_cpu_online(void) +{ + struct rcu_data *rdp; + struct rcu_node *rnp; + bool ret; + + if (in_nmi()) + return true; + preempt_disable(); + rdp = this_cpu_ptr(&rcu_sched_data); + rnp = rdp->mynode; + ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) || + !rcu_scheduler_fully_active; + preempt_enable(); + return ret; +} +EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); + +#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ + +/** + * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle + * + * If the current CPU is idle or running at a first-level (not nested) + * interrupt from idle, return true. The caller must have at least + * disabled preemption. + */ +static int rcu_is_cpu_rrupt_from_idle(void) +{ + return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1; +} + +/* + * Snapshot the specified CPU's dynticks counter so that we can later + * credit them with an implicit quiescent state. Return 1 if this CPU + * is in dynticks idle mode, which is an extended quiescent state. + */ +static int dyntick_save_progress_counter(struct rcu_data *rdp, + bool *isidle, unsigned long *maxj) +{ + rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks); + rcu_sysidle_check_cpu(rdp, isidle, maxj); + if ((rdp->dynticks_snap & 0x1) == 0) { + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); + return 1; + } else { + if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, + rdp->mynode->gpnum)) + WRITE_ONCE(rdp->gpwrap, true); + return 0; + } +} + +/* + * Return true if the specified CPU has passed through a quiescent + * state by virtue of being in or having passed through an dynticks + * idle state since the last call to dyntick_save_progress_counter() + * for this same CPU, or by virtue of having been offline. + */ +static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, + bool *isidle, unsigned long *maxj) +{ + unsigned int curr; + int *rcrmp; + unsigned int snap; + + curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks); + snap = (unsigned int)rdp->dynticks_snap; + + /* + * If the CPU passed through or entered a dynticks idle phase with + * no active irq/NMI handlers, then we can safely pretend that the CPU + * already acknowledged the request to pass through a quiescent + * state. Either way, that CPU cannot possibly be in an RCU + * read-side critical section that started before the beginning + * of the current RCU grace period. + */ + if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) { + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); + rdp->dynticks_fqs++; + return 1; + } + + /* + * Check for the CPU being offline, but only if the grace period + * is old enough. We don't need to worry about the CPU changing + * state: If we see it offline even once, it has been through a + * quiescent state. + * + * The reason for insisting that the grace period be at least + * one jiffy old is that CPUs that are not quite online and that + * have just gone offline can still execute RCU read-side critical + * sections. + */ + if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies)) + return 0; /* Grace period is not old enough. */ + barrier(); + if (cpu_is_offline(rdp->cpu)) { + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl")); + rdp->offline_fqs++; + return 1; + } + + /* + * A CPU running for an extended time within the kernel can + * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, + * even context-switching back and forth between a pair of + * in-kernel CPU-bound tasks cannot advance grace periods. + * So if the grace period is old enough, make the CPU pay attention. + * Note that the unsynchronized assignments to the per-CPU + * rcu_sched_qs_mask variable are safe. Yes, setting of + * bits can be lost, but they will be set again on the next + * force-quiescent-state pass. So lost bit sets do not result + * in incorrect behavior, merely in a grace period lasting + * a few jiffies longer than it might otherwise. Because + * there are at most four threads involved, and because the + * updates are only once every few jiffies, the probability of + * lossage (and thus of slight grace-period extension) is + * quite low. + * + * Note that if the jiffies_till_sched_qs boot/sysfs parameter + * is set too high, we override with half of the RCU CPU stall + * warning delay. + */ + rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu); + if (ULONG_CMP_GE(jiffies, + rdp->rsp->gp_start + jiffies_till_sched_qs) || + ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) { + if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) { + WRITE_ONCE(rdp->cond_resched_completed, + READ_ONCE(rdp->mynode->completed)); + smp_mb(); /* ->cond_resched_completed before *rcrmp. */ + WRITE_ONCE(*rcrmp, + READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask); + resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ + rdp->rsp->jiffies_resched += 5; /* Enable beating. */ + } else if (ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) { + /* Time to beat on that CPU again! */ + resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ + rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */ + } + } + + return 0; +} + +static void record_gp_stall_check_time(struct rcu_state *rsp) +{ + unsigned long j = jiffies; + unsigned long j1; + + rsp->gp_start = j; + smp_wmb(); /* Record start time before stall time. */ + j1 = rcu_jiffies_till_stall_check(); + WRITE_ONCE(rsp->jiffies_stall, j + j1); + rsp->jiffies_resched = j + j1 / 2; + rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs); +} + +/* + * Complain about starvation of grace-period kthread. + */ +static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp) +{ + unsigned long gpa; + unsigned long j; + + j = jiffies; + gpa = READ_ONCE(rsp->gp_activity); + if (j - gpa > 2 * HZ) + pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x s%d ->state=%#lx\n", + rsp->name, j - gpa, + rsp->gpnum, rsp->completed, + rsp->gp_flags, rsp->gp_state, + rsp->gp_kthread ? rsp->gp_kthread->state : 0); +} + +/* + * Dump stacks of all tasks running on stalled CPUs. + */ +static void rcu_dump_cpu_stacks(struct rcu_state *rsp) +{ + int cpu; + unsigned long flags; + struct rcu_node *rnp; + + rcu_for_each_leaf_node(rsp, rnp) { + raw_spin_lock_irqsave(&rnp->lock, flags); + if (rnp->qsmask != 0) { + for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) + if (rnp->qsmask & (1UL << cpu)) + dump_cpu_task(rnp->grplo + cpu); + } + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } +} + +static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) +{ + int cpu; + long delta; + unsigned long flags; + unsigned long gpa; + unsigned long j; + int ndetected = 0; + struct rcu_node *rnp = rcu_get_root(rsp); + long totqlen = 0; + + /* Only let one CPU complain about others per time interval. */ + + raw_spin_lock_irqsave(&rnp->lock, flags); + delta = jiffies - READ_ONCE(rsp->jiffies_stall); + if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + WRITE_ONCE(rsp->jiffies_stall, + jiffies + 3 * rcu_jiffies_till_stall_check() + 3); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + + /* + * OK, time to rat on our buddy... + * See Documentation/RCU/stallwarn.txt for info on how to debug + * RCU CPU stall warnings. + */ + pr_err("INFO: %s detected stalls on CPUs/tasks:", + rsp->name); + print_cpu_stall_info_begin(); + rcu_for_each_leaf_node(rsp, rnp) { + raw_spin_lock_irqsave(&rnp->lock, flags); + ndetected += rcu_print_task_stall(rnp); + if (rnp->qsmask != 0) { + for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) + if (rnp->qsmask & (1UL << cpu)) { + print_cpu_stall_info(rsp, + rnp->grplo + cpu); + ndetected++; + } + } + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } + + print_cpu_stall_info_end(); + for_each_possible_cpu(cpu) + totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen; + pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n", + smp_processor_id(), (long)(jiffies - rsp->gp_start), + (long)rsp->gpnum, (long)rsp->completed, totqlen); + if (ndetected) { + rcu_dump_cpu_stacks(rsp); + } else { + if (READ_ONCE(rsp->gpnum) != gpnum || + READ_ONCE(rsp->completed) == gpnum) { + pr_err("INFO: Stall ended before state dump start\n"); + } else { + j = jiffies; + gpa = READ_ONCE(rsp->gp_activity); + pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", + rsp->name, j - gpa, j, gpa, + jiffies_till_next_fqs, + rcu_get_root(rsp)->qsmask); + /* In this case, the current CPU might be at fault. */ + sched_show_task(current); + } + } + + /* Complain about tasks blocking the grace period. */ + rcu_print_detail_task_stall(rsp); + + rcu_check_gp_kthread_starvation(rsp); + +#ifdef CONFIG_RCU_STALL_WATCHDOG_BITE + /* Induce watchdog bite */ + msm_trigger_wdog_bite(); +#endif + + force_quiescent_state(rsp); /* Kick them all. */ +} + +static void print_cpu_stall(struct rcu_state *rsp) +{ + int cpu; + unsigned long flags; + struct rcu_node *rnp = rcu_get_root(rsp); + long totqlen = 0; + + /* + * OK, time to rat on ourselves... + * See Documentation/RCU/stallwarn.txt for info on how to debug + * RCU CPU stall warnings. + */ + pr_err("INFO: %s self-detected stall on CPU", rsp->name); + print_cpu_stall_info_begin(); + print_cpu_stall_info(rsp, smp_processor_id()); + print_cpu_stall_info_end(); + for_each_possible_cpu(cpu) + totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen; + pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n", + jiffies - rsp->gp_start, + (long)rsp->gpnum, (long)rsp->completed, totqlen); + + rcu_check_gp_kthread_starvation(rsp); + + rcu_dump_cpu_stacks(rsp); + + raw_spin_lock_irqsave(&rnp->lock, flags); + if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall))) + WRITE_ONCE(rsp->jiffies_stall, + jiffies + 3 * rcu_jiffies_till_stall_check() + 3); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + +#ifdef CONFIG_RCU_STALL_WATCHDOG_BITE + /* Induce non secure watchdog bite to collect context */ + msm_trigger_wdog_bite(); +#endif + + /* + * Attempt to revive the RCU machinery by forcing a context switch. + * + * A context switch would normally allow the RCU state machine to make + * progress and it could be we're stuck in kernel space without context + * switches for an entirely unreasonable amount of time. + */ + resched_cpu(smp_processor_id()); +} + +static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) +{ + unsigned long completed; + unsigned long gpnum; + unsigned long gps; + unsigned long j; + unsigned long js; + struct rcu_node *rnp; + + if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp)) + return; + j = jiffies; + + /* + * Lots of memory barriers to reject false positives. + * + * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall, + * then rsp->gp_start, and finally rsp->completed. These values + * are updated in the opposite order with memory barriers (or + * equivalent) during grace-period initialization and cleanup. + * Now, a false positive can occur if we get an new value of + * rsp->gp_start and a old value of rsp->jiffies_stall. But given + * the memory barriers, the only way that this can happen is if one + * grace period ends and another starts between these two fetches. + * Detect this by comparing rsp->completed with the previous fetch + * from rsp->gpnum. + * + * Given this check, comparisons of jiffies, rsp->jiffies_stall, + * and rsp->gp_start suffice to forestall false positives. + */ + gpnum = READ_ONCE(rsp->gpnum); + smp_rmb(); /* Pick up ->gpnum first... */ + js = READ_ONCE(rsp->jiffies_stall); + smp_rmb(); /* ...then ->jiffies_stall before the rest... */ + gps = READ_ONCE(rsp->gp_start); + smp_rmb(); /* ...and finally ->gp_start before ->completed. */ + completed = READ_ONCE(rsp->completed); + if (ULONG_CMP_GE(completed, gpnum) || + ULONG_CMP_LT(j, js) || + ULONG_CMP_GE(gps, js)) + return; /* No stall or GP completed since entering function. */ + rnp = rdp->mynode; + if (rcu_gp_in_progress(rsp) && + (READ_ONCE(rnp->qsmask) & rdp->grpmask)) { + + /* We haven't checked in, so go dump stack. */ + print_cpu_stall(rsp); + + } else if (rcu_gp_in_progress(rsp) && + ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) { + + /* They had a few time units to dump stack, so complain. */ + print_other_cpu_stall(rsp, gpnum); + } +} + +/** + * rcu_cpu_stall_reset - prevent further stall warnings in current grace period + * + * Set the stall-warning timeout way off into the future, thus preventing + * any RCU CPU stall-warning messages from appearing in the current set of + * RCU grace periods. + * + * The caller must disable hard irqs. + */ +void rcu_cpu_stall_reset(void) +{ + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) + WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2); +} + +/* + * Initialize the specified rcu_data structure's default callback list + * to empty. The default callback list is the one that is not used by + * no-callbacks CPUs. + */ +static void init_default_callback_list(struct rcu_data *rdp) +{ + int i; + + rdp->nxtlist = NULL; + for (i = 0; i < RCU_NEXT_SIZE; i++) + rdp->nxttail[i] = &rdp->nxtlist; +} + +/* + * Initialize the specified rcu_data structure's callback list to empty. + */ +static void init_callback_list(struct rcu_data *rdp) +{ + if (init_nocb_callback_list(rdp)) + return; + init_default_callback_list(rdp); +} + +/* + * Determine the value that ->completed will have at the end of the + * next subsequent grace period. This is used to tag callbacks so that + * a CPU can invoke callbacks in a timely fashion even if that CPU has + * been dyntick-idle for an extended period with callbacks under the + * influence of RCU_FAST_NO_HZ. + * + * The caller must hold rnp->lock with interrupts disabled. + */ +static unsigned long rcu_cbs_completed(struct rcu_state *rsp, + struct rcu_node *rnp) +{ + /* + * If RCU is idle, we just wait for the next grace period. + * But we can only be sure that RCU is idle if we are looking + * at the root rcu_node structure -- otherwise, a new grace + * period might have started, but just not yet gotten around + * to initializing the current non-root rcu_node structure. + */ + if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed) + return rnp->completed + 1; + + /* + * Otherwise, wait for a possible partial grace period and + * then the subsequent full grace period. + */ + return rnp->completed + 2; +} + +/* + * Trace-event helper function for rcu_start_future_gp() and + * rcu_nocb_wait_gp(). + */ +static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, + unsigned long c, const char *s) +{ + trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, + rnp->completed, c, rnp->level, + rnp->grplo, rnp->grphi, s); +} + +/* + * Start some future grace period, as needed to handle newly arrived + * callbacks. The required future grace periods are recorded in each + * rcu_node structure's ->need_future_gp field. Returns true if there + * is reason to awaken the grace-period kthread. + * + * The caller must hold the specified rcu_node structure's ->lock. + */ +static bool __maybe_unused +rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, + unsigned long *c_out) +{ + unsigned long c; + int i; + bool ret = false; + struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); + + /* + * Pick up grace-period number for new callbacks. If this + * grace period is already marked as needed, return to the caller. + */ + c = rcu_cbs_completed(rdp->rsp, rnp); + trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf")); + if (rnp->need_future_gp[c & 0x1]) { + trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf")); + goto out; + } + + /* + * If either this rcu_node structure or the root rcu_node structure + * believe that a grace period is in progress, then we must wait + * for the one following, which is in "c". Because our request + * will be noticed at the end of the current grace period, we don't + * need to explicitly start one. We only do the lockless check + * of rnp_root's fields if the current rcu_node structure thinks + * there is no grace period in flight, and because we hold rnp->lock, + * the only possible change is when rnp_root's two fields are + * equal, in which case rnp_root->gpnum might be concurrently + * incremented. But that is OK, as it will just result in our + * doing some extra useless work. + */ + if (rnp->gpnum != rnp->completed || + READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) { + rnp->need_future_gp[c & 0x1]++; + trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf")); + goto out; + } + + /* + * There might be no grace period in progress. If we don't already + * hold it, acquire the root rcu_node structure's lock in order to + * start one (if needed). + */ + if (rnp != rnp_root) { + raw_spin_lock(&rnp_root->lock); + smp_mb__after_unlock_lock(); + } + + /* + * Get a new grace-period number. If there really is no grace + * period in progress, it will be smaller than the one we obtained + * earlier. Adjust callbacks as needed. Note that even no-CBs + * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed. + */ + c = rcu_cbs_completed(rdp->rsp, rnp_root); + for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++) + if (ULONG_CMP_LT(c, rdp->nxtcompleted[i])) + rdp->nxtcompleted[i] = c; + + /* + * If the needed for the required grace period is already + * recorded, trace and leave. + */ + if (rnp_root->need_future_gp[c & 0x1]) { + trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot")); + goto unlock_out; + } + + /* Record the need for the future grace period. */ + rnp_root->need_future_gp[c & 0x1]++; + + /* If a grace period is not already in progress, start one. */ + if (rnp_root->gpnum != rnp_root->completed) { + trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot")); + } else { + trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot")); + ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp); + } +unlock_out: + if (rnp != rnp_root) + raw_spin_unlock(&rnp_root->lock); +out: + if (c_out != NULL) + *c_out = c; + return ret; +} + +/* + * Clean up any old requests for the just-ended grace period. Also return + * whether any additional grace periods have been requested. Also invoke + * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads + * waiting for this grace period to complete. + */ +static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +{ + int c = rnp->completed; + int needmore; + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); + + rcu_nocb_gp_cleanup(rsp, rnp); + rnp->need_future_gp[c & 0x1] = 0; + needmore = rnp->need_future_gp[(c + 1) & 0x1]; + trace_rcu_future_gp(rnp, rdp, c, + needmore ? TPS("CleanupMore") : TPS("Cleanup")); + return needmore; +} + +/* + * Awaken the grace-period kthread. Don't do a self-awaken (unless in + * an interrupt or softirq handler), and don't bother awakening when there + * is nothing for the grace-period kthread to do (as in several CPUs raced + * to awaken, and we lost), and finally don't try to awaken a kthread that + * has not yet been created. If all those checks are passed, track some + * debug information and awaken. + * + * So why do the self-wakeup when in an interrupt or softirq handler + * in the grace-period kthread's context? Because the kthread might have + * been interrupted just as it was going to sleep, and just after the final + * pre-sleep check of the awaken condition. In this case, a wakeup really + * is required, and is therefore supplied. + */ +static void rcu_gp_kthread_wake(struct rcu_state *rsp) +{ + if ((current == rsp->gp_kthread && + !in_interrupt() && !in_serving_softirq()) || + !READ_ONCE(rsp->gp_flags) || + !rsp->gp_kthread) + return; + wake_up(&rsp->gp_wq); +} + +/* + * If there is room, assign a ->completed number to any callbacks on + * this CPU that have not already been assigned. Also accelerate any + * callbacks that were previously assigned a ->completed number that has + * since proven to be too conservative, which can happen if callbacks get + * assigned a ->completed number while RCU is idle, but with reference to + * a non-root rcu_node structure. This function is idempotent, so it does + * not hurt to call it repeatedly. Returns an flag saying that we should + * awaken the RCU grace-period kthread. + * + * The caller must hold rnp->lock with interrupts disabled. + */ +static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp) +{ + unsigned long c; + int i; + bool ret; + + /* If the CPU has no callbacks, nothing to do. */ + if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL]) + return false; + + /* + * Starting from the sublist containing the callbacks most + * recently assigned a ->completed number and working down, find the + * first sublist that is not assignable to an upcoming grace period. + * Such a sublist has something in it (first two tests) and has + * a ->completed number assigned that will complete sooner than + * the ->completed number for newly arrived callbacks (last test). + * + * The key point is that any later sublist can be assigned the + * same ->completed number as the newly arrived callbacks, which + * means that the callbacks in any of these later sublist can be + * grouped into a single sublist, whether or not they have already + * been assigned a ->completed number. + */ + c = rcu_cbs_completed(rsp, rnp); + for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--) + if (rdp->nxttail[i] != rdp->nxttail[i - 1] && + !ULONG_CMP_GE(rdp->nxtcompleted[i], c)) + break; + + /* + * If there are no sublist for unassigned callbacks, leave. + * At the same time, advance "i" one sublist, so that "i" will + * index into the sublist where all the remaining callbacks should + * be grouped into. + */ + if (++i >= RCU_NEXT_TAIL) + return false; + + /* + * Assign all subsequent callbacks' ->completed number to the next + * full grace period and group them all in the sublist initially + * indexed by "i". + */ + for (; i <= RCU_NEXT_TAIL; i++) { + rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL]; + rdp->nxtcompleted[i] = c; + } + /* Record any needed additional grace periods. */ + ret = rcu_start_future_gp(rnp, rdp, NULL); + + /* Trace depending on how much we were able to accelerate. */ + if (!*rdp->nxttail[RCU_WAIT_TAIL]) + trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB")); + else + trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB")); + return ret; +} + +/* + * Move any callbacks whose grace period has completed to the + * RCU_DONE_TAIL sublist, then compact the remaining sublists and + * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL + * sublist. This function is idempotent, so it does not hurt to + * invoke it repeatedly. As long as it is not invoked -too- often... + * Returns true if the RCU grace-period kthread needs to be awakened. + * + * The caller must hold rnp->lock with interrupts disabled. + */ +static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp) +{ + int i, j; + + /* If the CPU has no callbacks, nothing to do. */ + if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL]) + return false; + + /* + * Find all callbacks whose ->completed numbers indicate that they + * are ready to invoke, and put them into the RCU_DONE_TAIL sublist. + */ + for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) { + if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i])) + break; + rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i]; + } + /* Clean up any sublist tail pointers that were misordered above. */ + for (j = RCU_WAIT_TAIL; j < i; j++) + rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL]; + + /* Copy down callbacks to fill in empty sublists. */ + for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) { + if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL]) + break; + rdp->nxttail[j] = rdp->nxttail[i]; + rdp->nxtcompleted[j] = rdp->nxtcompleted[i]; + } + + /* Classify any remaining callbacks. */ + return rcu_accelerate_cbs(rsp, rnp, rdp); +} + +/* + * Update CPU-local rcu_data state to record the beginnings and ends of + * grace periods. The caller must hold the ->lock of the leaf rcu_node + * structure corresponding to the current CPU, and must have irqs disabled. + * Returns true if the grace-period kthread needs to be awakened. + */ +static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp) +{ + bool ret; + + /* Handle the ends of any preceding grace periods first. */ + if (rdp->completed == rnp->completed && + !unlikely(READ_ONCE(rdp->gpwrap))) { + + /* No grace period end, so just accelerate recent callbacks. */ + ret = rcu_accelerate_cbs(rsp, rnp, rdp); + + } else { + + /* Advance callbacks. */ + ret = rcu_advance_cbs(rsp, rnp, rdp); + + /* Remember that we saw this grace-period completion. */ + rdp->completed = rnp->completed; + trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend")); + } + + if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) { + /* + * If the current grace period is waiting for this CPU, + * set up to detect a quiescent state, otherwise don't + * go looking for one. + */ + rdp->gpnum = rnp->gpnum; + trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart")); + rdp->cpu_no_qs.b.norm = true; + rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr); + rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask); + zero_cpu_stall_ticks(rdp); + WRITE_ONCE(rdp->gpwrap, false); + } + return ret; +} + +static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp) +{ + unsigned long flags; + bool needwake; + struct rcu_node *rnp; + + local_irq_save(flags); + rnp = rdp->mynode; + if ((rdp->gpnum == READ_ONCE(rnp->gpnum) && + rdp->completed == READ_ONCE(rnp->completed) && + !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */ + !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */ + local_irq_restore(flags); + return; + } + smp_mb__after_unlock_lock(); + needwake = __note_gp_changes(rsp, rnp, rdp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (needwake) + rcu_gp_kthread_wake(rsp); +} + +static void rcu_gp_slow(struct rcu_state *rsp, int delay) +{ + if (delay > 0 && + !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) + schedule_timeout_uninterruptible(delay); +} + +/* + * Initialize a new grace period. Return 0 if no grace period required. + */ +static int rcu_gp_init(struct rcu_state *rsp) +{ + unsigned long oldmask; + struct rcu_data *rdp; + struct rcu_node *rnp = rcu_get_root(rsp); + + WRITE_ONCE(rsp->gp_activity, jiffies); + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + if (!READ_ONCE(rsp->gp_flags)) { + /* Spurious wakeup, tell caller to go back to sleep. */ + raw_spin_unlock_irq(&rnp->lock); + return 0; + } + WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */ + + if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) { + /* + * Grace period already in progress, don't start another. + * Not supposed to be able to happen. + */ + raw_spin_unlock_irq(&rnp->lock); + return 0; + } + + /* Advance to a new grace period and initialize state. */ + record_gp_stall_check_time(rsp); + /* Record GP times before starting GP, hence smp_store_release(). */ + smp_store_release(&rsp->gpnum, rsp->gpnum + 1); + trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start")); + raw_spin_unlock_irq(&rnp->lock); + + /* + * Apply per-leaf buffered online and offline operations to the + * rcu_node tree. Note that this new grace period need not wait + * for subsequent online CPUs, and that quiescent-state forcing + * will handle subsequent offline CPUs. + */ + rcu_for_each_leaf_node(rsp, rnp) { + rcu_gp_slow(rsp, gp_preinit_delay); + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + if (rnp->qsmaskinit == rnp->qsmaskinitnext && + !rnp->wait_blkd_tasks) { + /* Nothing to do on this leaf rcu_node structure. */ + raw_spin_unlock_irq(&rnp->lock); + continue; + } + + /* Record old state, apply changes to ->qsmaskinit field. */ + oldmask = rnp->qsmaskinit; + rnp->qsmaskinit = rnp->qsmaskinitnext; + + /* If zero-ness of ->qsmaskinit changed, propagate up tree. */ + if (!oldmask != !rnp->qsmaskinit) { + if (!oldmask) /* First online CPU for this rcu_node. */ + rcu_init_new_rnp(rnp); + else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */ + rnp->wait_blkd_tasks = true; + else /* Last offline CPU and can propagate. */ + rcu_cleanup_dead_rnp(rnp); + } + + /* + * If all waited-on tasks from prior grace period are + * done, and if all this rcu_node structure's CPUs are + * still offline, propagate up the rcu_node tree and + * clear ->wait_blkd_tasks. Otherwise, if one of this + * rcu_node structure's CPUs has since come back online, + * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp() + * checks for this, so just call it unconditionally). + */ + if (rnp->wait_blkd_tasks && + (!rcu_preempt_has_tasks(rnp) || + rnp->qsmaskinit)) { + rnp->wait_blkd_tasks = false; + rcu_cleanup_dead_rnp(rnp); + } + + raw_spin_unlock_irq(&rnp->lock); + } + + /* + * Set the quiescent-state-needed bits in all the rcu_node + * structures for all currently online CPUs in breadth-first order, + * starting from the root rcu_node structure, relying on the layout + * of the tree within the rsp->node[] array. Note that other CPUs + * will access only the leaves of the hierarchy, thus seeing that no + * grace period is in progress, at least until the corresponding + * leaf node has been initialized. In addition, we have excluded + * CPU-hotplug operations. + * + * The grace period cannot complete until the initialization + * process finishes, because this kthread handles both. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + rcu_gp_slow(rsp, gp_init_delay); + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + rdp = this_cpu_ptr(rsp->rda); + rcu_preempt_check_blocked_tasks(rnp); + rnp->qsmask = rnp->qsmaskinit; + WRITE_ONCE(rnp->gpnum, rsp->gpnum); + if (WARN_ON_ONCE(rnp->completed != rsp->completed)) + WRITE_ONCE(rnp->completed, rsp->completed); + if (rnp == rdp->mynode) + (void)__note_gp_changes(rsp, rnp, rdp); + rcu_preempt_boost_start_gp(rnp); + trace_rcu_grace_period_init(rsp->name, rnp->gpnum, + rnp->level, rnp->grplo, + rnp->grphi, rnp->qsmask); + raw_spin_unlock_irq(&rnp->lock); + cond_resched_rcu_qs(); + WRITE_ONCE(rsp->gp_activity, jiffies); + } + + return 1; +} + +/* + * Helper function for wait_event_interruptible_timeout() wakeup + * at force-quiescent-state time. + */ +static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp) +{ + struct rcu_node *rnp = rcu_get_root(rsp); + + /* Someone like call_rcu() requested a force-quiescent-state scan. */ + *gfp = READ_ONCE(rsp->gp_flags); + if (*gfp & RCU_GP_FLAG_FQS) + return true; + + /* The current grace period has completed. */ + if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) + return true; + + return false; +} + +/* + * Do one round of quiescent-state forcing. + */ +static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time) +{ + bool isidle = false; + unsigned long maxj; + struct rcu_node *rnp = rcu_get_root(rsp); + + WRITE_ONCE(rsp->gp_activity, jiffies); + rsp->n_force_qs++; + if (first_time) { + /* Collect dyntick-idle snapshots. */ + if (is_sysidle_rcu_state(rsp)) { + isidle = true; + maxj = jiffies - ULONG_MAX / 4; + } + force_qs_rnp(rsp, dyntick_save_progress_counter, + &isidle, &maxj); + rcu_sysidle_report_gp(rsp, isidle, maxj); + } else { + /* Handle dyntick-idle and offline CPUs. */ + isidle = true; + force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj); + } + /* Clear flag to prevent immediate re-entry. */ + if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + WRITE_ONCE(rsp->gp_flags, + READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS); + raw_spin_unlock_irq(&rnp->lock); + } +} + +/* + * Clean up after the old grace period. + */ +static void rcu_gp_cleanup(struct rcu_state *rsp) +{ + unsigned long gp_duration; + bool needgp = false; + int nocb = 0; + struct rcu_data *rdp; + struct rcu_node *rnp = rcu_get_root(rsp); + + WRITE_ONCE(rsp->gp_activity, jiffies); + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + gp_duration = jiffies - rsp->gp_start; + if (gp_duration > rsp->gp_max) + rsp->gp_max = gp_duration; + + /* + * We know the grace period is complete, but to everyone else + * it appears to still be ongoing. But it is also the case + * that to everyone else it looks like there is nothing that + * they can do to advance the grace period. It is therefore + * safe for us to drop the lock in order to mark the grace + * period as completed in all of the rcu_node structures. + */ + raw_spin_unlock_irq(&rnp->lock); + + /* + * Propagate new ->completed value to rcu_node structures so + * that other CPUs don't have to wait until the start of the next + * grace period to process their callbacks. This also avoids + * some nasty RCU grace-period initialization races by forcing + * the end of the current grace period to be completely recorded in + * all of the rcu_node structures before the beginning of the next + * grace period is recorded in any of the rcu_node structures. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); + WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); + WARN_ON_ONCE(rnp->qsmask); + WRITE_ONCE(rnp->completed, rsp->gpnum); + rdp = this_cpu_ptr(rsp->rda); + if (rnp == rdp->mynode) + needgp = __note_gp_changes(rsp, rnp, rdp) || needgp; + /* smp_mb() provided by prior unlock-lock pair. */ + nocb += rcu_future_gp_cleanup(rsp, rnp); + raw_spin_unlock_irq(&rnp->lock); + cond_resched_rcu_qs(); + WRITE_ONCE(rsp->gp_activity, jiffies); + rcu_gp_slow(rsp, gp_cleanup_delay); + } + rnp = rcu_get_root(rsp); + raw_spin_lock_irq(&rnp->lock); + smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */ + rcu_nocb_gp_set(rnp, nocb); + + /* Declare grace period done. */ + WRITE_ONCE(rsp->completed, rsp->gpnum); + trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end")); + rsp->gp_state = RCU_GP_IDLE; + rdp = this_cpu_ptr(rsp->rda); + /* Advance CBs to reduce false positives below. */ + needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp; + if (needgp || cpu_needs_another_gp(rsp, rdp)) { + WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("newreq")); + } + raw_spin_unlock_irq(&rnp->lock); +} + +/* + * Body of kthread that handles grace periods. + */ +static int __noreturn rcu_gp_kthread(void *arg) +{ + bool first_gp_fqs; + int gf; + unsigned long j; + int ret; + struct rcu_state *rsp = arg; + struct rcu_node *rnp = rcu_get_root(rsp); + + rcu_bind_gp_kthread(); + for (;;) { + + /* Handle grace-period start. */ + for (;;) { + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("reqwait")); + rsp->gp_state = RCU_GP_WAIT_GPS; + wait_event_interruptible(rsp->gp_wq, + READ_ONCE(rsp->gp_flags) & + RCU_GP_FLAG_INIT); + rsp->gp_state = RCU_GP_DONE_GPS; + /* Locking provides needed memory barrier. */ + if (rcu_gp_init(rsp)) + break; + cond_resched_rcu_qs(); + WRITE_ONCE(rsp->gp_activity, jiffies); + WARN_ON(signal_pending(current)); + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("reqwaitsig")); + } + + /* Handle quiescent-state forcing. */ + first_gp_fqs = true; + j = jiffies_till_first_fqs; + if (j > HZ) { + j = HZ; + jiffies_till_first_fqs = HZ; + } + ret = 0; + for (;;) { + if (!ret) + rsp->jiffies_force_qs = jiffies + j; + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("fqswait")); + rsp->gp_state = RCU_GP_WAIT_FQS; + ret = wait_event_interruptible_timeout(rsp->gp_wq, + rcu_gp_fqs_check_wake(rsp, &gf), j); + rsp->gp_state = RCU_GP_DOING_FQS; + /* Locking provides needed memory barriers. */ + /* If grace period done, leave loop. */ + if (!READ_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)) + break; + /* If time for quiescent-state forcing, do it. */ + if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) || + (gf & RCU_GP_FLAG_FQS)) { + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("fqsstart")); + rcu_gp_fqs(rsp, first_gp_fqs); + first_gp_fqs = false; + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("fqsend")); + cond_resched_rcu_qs(); + WRITE_ONCE(rsp->gp_activity, jiffies); + } else { + /* Deal with stray signal. */ + cond_resched_rcu_qs(); + WRITE_ONCE(rsp->gp_activity, jiffies); + WARN_ON(signal_pending(current)); + trace_rcu_grace_period(rsp->name, + READ_ONCE(rsp->gpnum), + TPS("fqswaitsig")); + } + j = jiffies_till_next_fqs; + if (j > HZ) { + j = HZ; + jiffies_till_next_fqs = HZ; + } else if (j < 1) { + j = 1; + jiffies_till_next_fqs = 1; + } + } + + /* Handle grace-period end. */ + rsp->gp_state = RCU_GP_CLEANUP; + rcu_gp_cleanup(rsp); + rsp->gp_state = RCU_GP_CLEANED; + } +} + +/* + * Start a new RCU grace period if warranted, re-initializing the hierarchy + * in preparation for detecting the next grace period. The caller must hold + * the root node's ->lock and hard irqs must be disabled. + * + * Note that it is legal for a dying CPU (which is marked as offline) to + * invoke this function. This can happen when the dying CPU reports its + * quiescent state. + * + * Returns true if the grace-period kthread must be awakened. + */ +static bool +rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp) +{ + if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { + /* + * Either we have not yet spawned the grace-period + * task, this CPU does not need another grace period, + * or a grace period is already in progress. + * Either way, don't start a new grace period. + */ + return false; + } + WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); + trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), + TPS("newreq")); + + /* + * We can't do wakeups while holding the rnp->lock, as that + * could cause possible deadlocks with the rq->lock. Defer + * the wakeup to our caller. + */ + return true; +} + +/* + * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's + * callbacks. Note that rcu_start_gp_advanced() cannot do this because it + * is invoked indirectly from rcu_advance_cbs(), which would result in + * endless recursion -- or would do so if it wasn't for the self-deadlock + * that is encountered beforehand. + * + * Returns true if the grace-period kthread needs to be awakened. + */ +static bool rcu_start_gp(struct rcu_state *rsp) +{ + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); + struct rcu_node *rnp = rcu_get_root(rsp); + bool ret = false; + + /* + * If there is no grace period in progress right now, any + * callbacks we have up to this point will be satisfied by the + * next grace period. Also, advancing the callbacks reduces the + * probability of false positives from cpu_needs_another_gp() + * resulting in pointless grace periods. So, advance callbacks + * then start the grace period! + */ + ret = rcu_advance_cbs(rsp, rnp, rdp) || ret; + ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret; + return ret; +} + +/* + * Report a full set of quiescent states to the specified rcu_state + * data structure. This involves cleaning up after the prior grace + * period and letting rcu_start_gp() start up the next grace period + * if one is needed. Note that the caller must hold rnp->lock, which + * is released before return. + */ +static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) + __releases(rcu_get_root(rsp)->lock) +{ + WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); + WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); + rcu_gp_kthread_wake(rsp); +} + +/* + * Similar to rcu_report_qs_rdp(), for which it is a helper function. + * Allows quiescent states for a group of CPUs to be reported at one go + * to the specified rcu_node structure, though all the CPUs in the group + * must be represented by the same rcu_node structure (which need not be a + * leaf rcu_node structure, though it often will be). The gps parameter + * is the grace-period snapshot, which means that the quiescent states + * are valid only if rnp->gpnum is equal to gps. That structure's lock + * must be held upon entry, and it is released before return. + */ +static void +rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, + struct rcu_node *rnp, unsigned long gps, unsigned long flags) + __releases(rnp->lock) +{ + unsigned long oldmask = 0; + struct rcu_node *rnp_c; + + /* Walk up the rcu_node hierarchy. */ + for (;;) { + if (!(rnp->qsmask & mask) || rnp->gpnum != gps) { + + /* + * Our bit has already been cleared, or the + * relevant grace period is already over, so done. + */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ + rnp->qsmask &= ~mask; + trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum, + mask, rnp->qsmask, rnp->level, + rnp->grplo, rnp->grphi, + !!rnp->gp_tasks); + if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { + + /* Other bits still set at this level, so done. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + mask = rnp->grpmask; + if (rnp->parent == NULL) { + + /* No more levels. Exit loop holding root lock. */ + + break; + } + raw_spin_unlock_irqrestore(&rnp->lock, flags); + rnp_c = rnp; + rnp = rnp->parent; + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + oldmask = rnp_c->qsmask; + } + + /* + * Get here if we are the last CPU to pass through a quiescent + * state for this grace period. Invoke rcu_report_qs_rsp() + * to clean up and start the next grace period if one is needed. + */ + rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */ +} + +/* + * Record a quiescent state for all tasks that were previously queued + * on the specified rcu_node structure and that were blocking the current + * RCU grace period. The caller must hold the specified rnp->lock with + * irqs disabled, and this lock is released upon return, but irqs remain + * disabled. + */ +static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp, + struct rcu_node *rnp, unsigned long flags) + __releases(rnp->lock) +{ + unsigned long gps; + unsigned long mask; + struct rcu_node *rnp_p; + + if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p || + rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; /* Still need more quiescent states! */ + } + + rnp_p = rnp->parent; + if (rnp_p == NULL) { + /* + * Only one rcu_node structure in the tree, so don't + * try to report up to its nonexistent parent! + */ + rcu_report_qs_rsp(rsp, flags); + return; + } + + /* Report up the rest of the hierarchy, tracking current ->gpnum. */ + gps = rnp->gpnum; + mask = rnp->grpmask; + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ + smp_mb__after_unlock_lock(); + rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags); +} + +/* + * Record a quiescent state for the specified CPU to that CPU's rcu_data + * structure. This must be either called from the specified CPU, or + * called when the specified CPU is known to be offline (and when it is + * also known that no other CPU is concurrently trying to help the offline + * CPU). The lastcomp argument is used to make sure we are still in the + * grace period of interest. We don't want to end the current grace period + * based on quiescent states detected in an earlier grace period! + */ +static void +rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) +{ + unsigned long flags; + unsigned long mask; + bool needwake; + struct rcu_node *rnp; + + rnp = rdp->mynode; + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + if ((rdp->cpu_no_qs.b.norm && + rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) || + rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum || + rdp->gpwrap) { + + /* + * The grace period in which this quiescent state was + * recorded has ended, so don't report it upwards. + * We will instead need a new quiescent state that lies + * within the current grace period. + */ + rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */ + rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + mask = rdp->grpmask; + if ((rnp->qsmask & mask) == 0) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } else { + rdp->core_needs_qs = 0; + + /* + * This GP can't end until cpu checks in, so all of our + * callbacks can be processed during the next GP. + */ + needwake = rcu_accelerate_cbs(rsp, rnp, rdp); + + rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); + /* ^^^ Released rnp->lock */ + if (needwake) + rcu_gp_kthread_wake(rsp); + } +} + +/* + * Check to see if there is a new grace period of which this CPU + * is not yet aware, and if so, set up local rcu_data state for it. + * Otherwise, see if this CPU has just passed through its first + * quiescent state for this grace period, and record that fact if so. + */ +static void +rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) +{ + /* Check for grace-period ends and beginnings. */ + note_gp_changes(rsp, rdp); + + /* + * Does this CPU still need to do its part for current grace period? + * If no, return and let the other CPUs do their part as well. + */ + if (!rdp->core_needs_qs) + return; + + /* + * Was there a quiescent state since the beginning of the grace + * period? If no, then exit and wait for the next call. + */ + if (rdp->cpu_no_qs.b.norm && + rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) + return; + + /* + * Tell RCU we are done (but rcu_report_qs_rdp() will be the + * judge of that). + */ + rcu_report_qs_rdp(rdp->cpu, rsp, rdp); +} + +/* + * Send the specified CPU's RCU callbacks to the orphanage. The + * specified CPU must be offline, and the caller must hold the + * ->orphan_lock. + */ +static void +rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp, + struct rcu_node *rnp, struct rcu_data *rdp) +{ + /* No-CBs CPUs do not have orphanable callbacks. */ + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu)) + return; + + /* + * Orphan the callbacks. First adjust the counts. This is safe + * because _rcu_barrier() excludes CPU-hotplug operations, so it + * cannot be running now. Thus no memory barrier is required. + */ + if (rdp->nxtlist != NULL) { + rsp->qlen_lazy += rdp->qlen_lazy; + rsp->qlen += rdp->qlen; + rdp->n_cbs_orphaned += rdp->qlen; + rdp->qlen_lazy = 0; + WRITE_ONCE(rdp->qlen, 0); + } + + /* + * Next, move those callbacks still needing a grace period to + * the orphanage, where some other CPU will pick them up. + * Some of the callbacks might have gone partway through a grace + * period, but that is too bad. They get to start over because we + * cannot assume that grace periods are synchronized across CPUs. + * We don't bother updating the ->nxttail[] array yet, instead + * we just reset the whole thing later on. + */ + if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) { + *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL]; + rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL]; + *rdp->nxttail[RCU_DONE_TAIL] = NULL; + } + + /* + * Then move the ready-to-invoke callbacks to the orphanage, + * where some other CPU will pick them up. These will not be + * required to pass though another grace period: They are done. + */ + if (rdp->nxtlist != NULL) { + *rsp->orphan_donetail = rdp->nxtlist; + rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL]; + } + + /* + * Finally, initialize the rcu_data structure's list to empty and + * disallow further callbacks on this CPU. + */ + init_callback_list(rdp); + rdp->nxttail[RCU_NEXT_TAIL] = NULL; +} + +/* + * Adopt the RCU callbacks from the specified rcu_state structure's + * orphanage. The caller must hold the ->orphan_lock. + */ +static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags) +{ + int i; + struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); + + /* No-CBs CPUs are handled specially. */ + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || + rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags)) + return; + + /* Do the accounting first. */ + rdp->qlen_lazy += rsp->qlen_lazy; + rdp->qlen += rsp->qlen; + rdp->n_cbs_adopted += rsp->qlen; + if (rsp->qlen_lazy != rsp->qlen) + rcu_idle_count_callbacks_posted(); + rsp->qlen_lazy = 0; + rsp->qlen = 0; + + /* + * We do not need a memory barrier here because the only way we + * can get here if there is an rcu_barrier() in flight is if + * we are the task doing the rcu_barrier(). + */ + + /* First adopt the ready-to-invoke callbacks. */ + if (rsp->orphan_donelist != NULL) { + *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL]; + *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist; + for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--) + if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) + rdp->nxttail[i] = rsp->orphan_donetail; + rsp->orphan_donelist = NULL; + rsp->orphan_donetail = &rsp->orphan_donelist; + } + + /* And then adopt the callbacks that still need a grace period. */ + if (rsp->orphan_nxtlist != NULL) { + *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist; + rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail; + rsp->orphan_nxtlist = NULL; + rsp->orphan_nxttail = &rsp->orphan_nxtlist; + } +} + +/* + * Trace the fact that this CPU is going offline. + */ +static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) +{ + RCU_TRACE(unsigned long mask); + RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda)); + RCU_TRACE(struct rcu_node *rnp = rdp->mynode); + + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) + return; + + RCU_TRACE(mask = rdp->grpmask); + trace_rcu_grace_period(rsp->name, + rnp->gpnum + 1 - !!(rnp->qsmask & mask), + TPS("cpuofl")); +} + +/* + * All CPUs for the specified rcu_node structure have gone offline, + * and all tasks that were preempted within an RCU read-side critical + * section while running on one of those CPUs have since exited their RCU + * read-side critical section. Some other CPU is reporting this fact with + * the specified rcu_node structure's ->lock held and interrupts disabled. + * This function therefore goes up the tree of rcu_node structures, + * clearing the corresponding bits in the ->qsmaskinit fields. Note that + * the leaf rcu_node structure's ->qsmaskinit field has already been + * updated + * + * This function does check that the specified rcu_node structure has + * all CPUs offline and no blocked tasks, so it is OK to invoke it + * prematurely. That said, invoking it after the fact will cost you + * a needless lock acquisition. So once it has done its work, don't + * invoke it again. + */ +static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) +{ + long mask; + struct rcu_node *rnp = rnp_leaf; + + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || + rnp->qsmaskinit || rcu_preempt_has_tasks(rnp)) + return; + for (;;) { + mask = rnp->grpmask; + rnp = rnp->parent; + if (!rnp) + break; + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + smp_mb__after_unlock_lock(); /* GP memory ordering. */ + rnp->qsmaskinit &= ~mask; + rnp->qsmask &= ~mask; + if (rnp->qsmaskinit) { + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + return; + } + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + } +} + +/* + * The CPU is exiting the idle loop into the arch_cpu_idle_dead() + * function. We now remove it from the rcu_node tree's ->qsmaskinit + * bit masks. + */ +static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp) +{ + unsigned long flags; + unsigned long mask; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ + + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) + return; + + /* Remove outgoing CPU from mask in the leaf rcu_node structure. */ + mask = rdp->grpmask; + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); /* Enforce GP memory-order guarantee. */ + rnp->qsmaskinitnext &= ~mask; + raw_spin_unlock_irqrestore(&rnp->lock, flags); +} + +/* + * The CPU has been completely removed, and some other CPU is reporting + * this fact from process context. Do the remainder of the cleanup, + * including orphaning the outgoing CPU's RCU callbacks, and also + * adopting them. There can only be one CPU hotplug operation at a time, + * so no other CPU can be attempting to update rcu_cpu_kthread_task. + */ +static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) +{ + unsigned long flags; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ + + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) + return; + + /* Adjust any no-longer-needed kthreads. */ + rcu_boost_kthread_setaffinity(rnp, -1); + + /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */ + raw_spin_lock_irqsave(&rsp->orphan_lock, flags); + rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp); + rcu_adopt_orphan_cbs(rsp, flags); + raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags); + + WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL, + "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n", + cpu, rdp->qlen, rdp->nxtlist); +} + +/* + * Invoke any RCU callbacks that have made it to the end of their grace + * period. Thottle as specified by rdp->blimit. + */ +static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) +{ + unsigned long flags; + struct rcu_head *next, *list, **tail; + long bl, count, count_lazy; + int i; + + /* If no callbacks are ready, just return. */ + if (!cpu_has_callbacks_ready_to_invoke(rdp)) { + trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0); + trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist), + need_resched(), is_idle_task(current), + rcu_is_callbacks_kthread()); + return; + } + + /* + * Extract the list of ready callbacks, disabling to prevent + * races with call_rcu() from interrupt handlers. + */ + local_irq_save(flags); + WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); + bl = rdp->blimit; + trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl); + list = rdp->nxtlist; + rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; + *rdp->nxttail[RCU_DONE_TAIL] = NULL; + tail = rdp->nxttail[RCU_DONE_TAIL]; + for (i = RCU_NEXT_SIZE - 1; i >= 0; i--) + if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) + rdp->nxttail[i] = &rdp->nxtlist; + local_irq_restore(flags); + + /* Invoke callbacks. */ + count = count_lazy = 0; + while (list) { + next = list->next; + prefetch(next); + debug_rcu_head_unqueue(list); + if (__rcu_reclaim(rsp->name, list)) + count_lazy++; + list = next; + /* Stop only if limit reached and CPU has something to do. */ + if (++count >= bl && + (need_resched() || + (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) + break; + } + + local_irq_save(flags); + trace_rcu_batch_end(rsp->name, count, !!list, need_resched(), + is_idle_task(current), + rcu_is_callbacks_kthread()); + + /* Update count, and requeue any remaining callbacks. */ + if (list != NULL) { + *tail = rdp->nxtlist; + rdp->nxtlist = list; + for (i = 0; i < RCU_NEXT_SIZE; i++) + if (&rdp->nxtlist == rdp->nxttail[i]) + rdp->nxttail[i] = tail; + else + break; + } + smp_mb(); /* List handling before counting for rcu_barrier(). */ + rdp->qlen_lazy -= count_lazy; + WRITE_ONCE(rdp->qlen, rdp->qlen - count); + rdp->n_cbs_invoked += count; + + /* Reinstate batch limit if we have worked down the excess. */ + if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark) + rdp->blimit = blimit; + + /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ + if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) { + rdp->qlen_last_fqs_check = 0; + rdp->n_force_qs_snap = rsp->n_force_qs; + } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark) + rdp->qlen_last_fqs_check = rdp->qlen; + WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0)); + + local_irq_restore(flags); + + /* Re-invoke RCU core processing if there are callbacks remaining. */ + if (cpu_has_callbacks_ready_to_invoke(rdp)) + invoke_rcu_core(); +} + +/* + * Check to see if this CPU is in a non-context-switch quiescent state + * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). + * Also schedule RCU core processing. + * + * This function must be called from hardirq context. It is normally + * invoked from the scheduling-clock interrupt. If rcu_pending returns + * false, there is no point in invoking rcu_check_callbacks(). + */ +void rcu_check_callbacks(int user) +{ + trace_rcu_utilization(TPS("Start scheduler-tick")); + increment_cpu_stall_ticks(); + if (user || rcu_is_cpu_rrupt_from_idle()) { + + /* + * Get here if this CPU took its interrupt from user + * mode or from the idle loop, and if this is not a + * nested interrupt. In this case, the CPU is in + * a quiescent state, so note it. + * + * No memory barrier is required here because both + * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local + * variables that other CPUs neither access nor modify, + * at least not while the corresponding CPU is online. + */ + + rcu_sched_qs(); + rcu_bh_qs(); + + } else if (!in_softirq()) { + + /* + * Get here if this CPU did not take its interrupt from + * softirq, in other words, if it is not interrupting + * a rcu_bh read-side critical section. This is an _bh + * critical section, so note it. + */ + + rcu_bh_qs(); + } + rcu_preempt_check_callbacks(); + if (rcu_pending()) + invoke_rcu_core(); + if (user) + rcu_note_voluntary_context_switch(current); + trace_rcu_utilization(TPS("End scheduler-tick")); +} + +/* + * Scan the leaf rcu_node structures, processing dyntick state for any that + * have not yet encountered a quiescent state, using the function specified. + * Also initiate boosting for any threads blocked on the root rcu_node. + * + * The caller must have suppressed start of new grace periods. + */ +static void force_qs_rnp(struct rcu_state *rsp, + int (*f)(struct rcu_data *rsp, bool *isidle, + unsigned long *maxj), + bool *isidle, unsigned long *maxj) +{ + unsigned long bit; + int cpu; + unsigned long flags; + unsigned long mask; + struct rcu_node *rnp; + + rcu_for_each_leaf_node(rsp, rnp) { + cond_resched_rcu_qs(); + mask = 0; + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + if (rnp->qsmask == 0) { + if (rcu_state_p == &rcu_sched_state || + rsp != rcu_state_p || + rcu_preempt_blocked_readers_cgp(rnp)) { + /* + * No point in scanning bits because they + * are all zero. But we might need to + * priority-boost blocked readers. + */ + rcu_initiate_boost(rnp, flags); + /* rcu_initiate_boost() releases rnp->lock */ + continue; + } + if (rnp->parent && + (rnp->parent->qsmask & rnp->grpmask)) { + /* + * Race between grace-period + * initialization and task exiting RCU + * read-side critical section: Report. + */ + rcu_report_unblock_qs_rnp(rsp, rnp, flags); + /* rcu_report_unblock_qs_rnp() rlses ->lock */ + continue; + } + } + cpu = rnp->grplo; + bit = 1; + for (; cpu <= rnp->grphi; cpu++, bit <<= 1) { + if ((rnp->qsmask & bit) != 0) { + if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj)) + mask |= bit; + } + } + if (mask != 0) { + /* Idle/offline CPUs, report (releases rnp->lock. */ + rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); + } else { + /* Nothing to do here, so just drop the lock. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } + } +} + +/* + * Force quiescent states on reluctant CPUs, and also detect which + * CPUs are in dyntick-idle mode. + */ +static void force_quiescent_state(struct rcu_state *rsp) +{ + unsigned long flags; + bool ret; + struct rcu_node *rnp; + struct rcu_node *rnp_old = NULL; + + /* Funnel through hierarchy to reduce memory contention. */ + rnp = __this_cpu_read(rsp->rda->mynode); + for (; rnp != NULL; rnp = rnp->parent) { + ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) || + !raw_spin_trylock(&rnp->fqslock); + if (rnp_old != NULL) + raw_spin_unlock(&rnp_old->fqslock); + if (ret) { + rsp->n_force_qs_lh++; + return; + } + rnp_old = rnp; + } + /* rnp_old == rcu_get_root(rsp), rnp == NULL. */ + + /* Reached the root of the rcu_node tree, acquire lock. */ + raw_spin_lock_irqsave(&rnp_old->lock, flags); + smp_mb__after_unlock_lock(); + raw_spin_unlock(&rnp_old->fqslock); + if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { + rsp->n_force_qs_lh++; + raw_spin_unlock_irqrestore(&rnp_old->lock, flags); + return; /* Someone beat us to it. */ + } + WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); + raw_spin_unlock_irqrestore(&rnp_old->lock, flags); + rcu_gp_kthread_wake(rsp); +} + +/* + * This does the RCU core processing work for the specified rcu_state + * and rcu_data structures. This may be called only from the CPU to + * whom the rdp belongs. + */ +static void +__rcu_process_callbacks(struct rcu_state *rsp) +{ + unsigned long flags; + bool needwake; + struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); + + WARN_ON_ONCE(rdp->beenonline == 0); + + /* Update RCU state based on any recent quiescent states. */ + rcu_check_quiescent_state(rsp, rdp); + + /* Does this CPU require a not-yet-started grace period? */ + local_irq_save(flags); + if (cpu_needs_another_gp(rsp, rdp)) { + raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */ + needwake = rcu_start_gp(rsp); + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); + if (needwake) + rcu_gp_kthread_wake(rsp); + } else { + local_irq_restore(flags); + } + + /* If there are callbacks ready, invoke them. */ + if (cpu_has_callbacks_ready_to_invoke(rdp)) + invoke_rcu_callbacks(rsp, rdp); + + /* Do any needed deferred wakeups of rcuo kthreads. */ + do_nocb_deferred_wakeup(rdp); +} + +/* + * Do RCU core processing for the current CPU. + */ +static void rcu_process_callbacks(struct softirq_action *unused) +{ + struct rcu_state *rsp; + + if (cpu_is_offline(smp_processor_id())) + return; + trace_rcu_utilization(TPS("Start RCU core")); + for_each_rcu_flavor(rsp) + __rcu_process_callbacks(rsp); + trace_rcu_utilization(TPS("End RCU core")); +} + +/* + * Schedule RCU callback invocation. If the specified type of RCU + * does not support RCU priority boosting, just do a direct call, + * otherwise wake up the per-CPU kernel kthread. Note that because we + * are running on the current CPU with softirqs disabled, the + * rcu_cpu_kthread_task cannot disappear out from under us. + */ +static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) +{ + if (unlikely(!READ_ONCE(rcu_scheduler_fully_active))) + return; + if (likely(!rsp->boost)) { + rcu_do_batch(rsp, rdp); + return; + } + invoke_rcu_callbacks_kthread(); +} + +static void invoke_rcu_core(void) +{ + if (cpu_online(smp_processor_id())) + raise_softirq(RCU_SOFTIRQ); +} + +/* + * Handle any core-RCU processing required by a call_rcu() invocation. + */ +static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, + struct rcu_head *head, unsigned long flags) +{ + bool needwake; + + /* + * If called from an extended quiescent state, invoke the RCU + * core in order to force a re-evaluation of RCU's idleness. + */ + if (!rcu_is_watching()) + invoke_rcu_core(); + + /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ + if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) + return; + + /* + * Force the grace period if too many callbacks or too long waiting. + * Enforce hysteresis, and don't invoke force_quiescent_state() + * if some other CPU has recently done so. Also, don't bother + * invoking force_quiescent_state() if the newly enqueued callback + * is the only one waiting for a grace period to complete. + */ + if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { + + /* Are we ignoring a completed grace period? */ + note_gp_changes(rsp, rdp); + + /* Start a new grace period if one not already started. */ + if (!rcu_gp_in_progress(rsp)) { + struct rcu_node *rnp_root = rcu_get_root(rsp); + + raw_spin_lock(&rnp_root->lock); + smp_mb__after_unlock_lock(); + needwake = rcu_start_gp(rsp); + raw_spin_unlock(&rnp_root->lock); + if (needwake) + rcu_gp_kthread_wake(rsp); + } else { + /* Give the grace period a kick. */ + rdp->blimit = LONG_MAX; + if (rsp->n_force_qs == rdp->n_force_qs_snap && + *rdp->nxttail[RCU_DONE_TAIL] != head) + force_quiescent_state(rsp); + rdp->n_force_qs_snap = rsp->n_force_qs; + rdp->qlen_last_fqs_check = rdp->qlen; + } + } +} + +/* + * RCU callback function to leak a callback. + */ +static void rcu_leak_callback(struct rcu_head *rhp) +{ +} + +/* + * Helper function for call_rcu() and friends. The cpu argument will + * normally be -1, indicating "currently running CPU". It may specify + * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier() + * is expected to specify a CPU. + */ +static void +__call_rcu(struct rcu_head *head, rcu_callback_t func, + struct rcu_state *rsp, int cpu, bool lazy) +{ + unsigned long flags; + struct rcu_data *rdp; + + WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */ + if (debug_rcu_head_queue(head)) { + /* Probable double call_rcu(), so leak the callback. */ + WRITE_ONCE(head->func, rcu_leak_callback); + WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n"); + return; + } + head->func = func; + head->next = NULL; + + /* + * Opportunistically note grace-period endings and beginnings. + * Note that we might see a beginning right after we see an + * end, but never vice versa, since this CPU has to pass through + * a quiescent state betweentimes. + */ + local_irq_save(flags); + rdp = this_cpu_ptr(rsp->rda); + + /* Add the callback to our list. */ + if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) { + int offline; + + if (cpu != -1) + rdp = per_cpu_ptr(rsp->rda, cpu); + if (likely(rdp->mynode)) { + /* Post-boot, so this should be for a no-CBs CPU. */ + offline = !__call_rcu_nocb(rdp, head, lazy, flags); + WARN_ON_ONCE(offline); + /* Offline CPU, _call_rcu() illegal, leak callback. */ + local_irq_restore(flags); + return; + } + /* + * Very early boot, before rcu_init(). Initialize if needed + * and then drop through to queue the callback. + */ + BUG_ON(cpu != -1); + WARN_ON_ONCE(!rcu_is_watching()); + if (!likely(rdp->nxtlist)) + init_default_callback_list(rdp); + } + WRITE_ONCE(rdp->qlen, rdp->qlen + 1); + if (lazy) + rdp->qlen_lazy++; + else + rcu_idle_count_callbacks_posted(); + smp_mb(); /* Count before adding callback for rcu_barrier(). */ + *rdp->nxttail[RCU_NEXT_TAIL] = head; + rdp->nxttail[RCU_NEXT_TAIL] = &head->next; + + if (__is_kfree_rcu_offset((unsigned long)func)) + trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func, + rdp->qlen_lazy, rdp->qlen); + else + trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen); + + /* Go handle any RCU core processing required. */ + __call_rcu_core(rsp, rdp, head, flags); + local_irq_restore(flags); +} + +/* + * Queue an RCU-sched callback for invocation after a grace period. + */ +void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) +{ + __call_rcu(head, func, &rcu_sched_state, -1, 0); +} +EXPORT_SYMBOL_GPL(call_rcu_sched); + +/* + * Queue an RCU callback for invocation after a quicker grace period. + */ +void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) +{ + __call_rcu(head, func, &rcu_bh_state, -1, 0); +} +EXPORT_SYMBOL_GPL(call_rcu_bh); + +/* + * Queue an RCU callback for lazy invocation after a grace period. + * This will likely be later named something like "call_rcu_lazy()", + * but this change will require some way of tagging the lazy RCU + * callbacks in the list of pending callbacks. Until then, this + * function may only be called from __kfree_rcu(). + */ +void kfree_call_rcu(struct rcu_head *head, + rcu_callback_t func) +{ + __call_rcu(head, func, rcu_state_p, -1, 1); +} +EXPORT_SYMBOL_GPL(kfree_call_rcu); + +/* + * Because a context switch is a grace period for RCU-sched and RCU-bh, + * any blocking grace-period wait automatically implies a grace period + * if there is only one CPU online at any point time during execution + * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to + * occasionally incorrectly indicate that there are multiple CPUs online + * when there was in fact only one the whole time, as this just adds + * some overhead: RCU still operates correctly. + */ +static inline int rcu_blocking_is_gp(void) +{ + int ret; + + might_sleep(); /* Check for RCU read-side critical section. */ + preempt_disable(); + ret = num_online_cpus() <= 1; + preempt_enable(); + return ret; +} + +/** + * synchronize_sched - wait until an rcu-sched grace period has elapsed. + * + * Control will return to the caller some time after a full rcu-sched + * grace period has elapsed, in other words after all currently executing + * rcu-sched read-side critical sections have completed. These read-side + * critical sections are delimited by rcu_read_lock_sched() and + * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), + * local_irq_disable(), and so on may be used in place of + * rcu_read_lock_sched(). + * + * This means that all preempt_disable code sequences, including NMI and + * non-threaded hardware-interrupt handlers, in progress on entry will + * have completed before this primitive returns. However, this does not + * guarantee that softirq handlers will have completed, since in some + * kernels, these handlers can run in process context, and can block. + * + * Note that this guarantee implies further memory-ordering guarantees. + * On systems with more than one CPU, when synchronize_sched() returns, + * each CPU is guaranteed to have executed a full memory barrier since the + * end of its last RCU-sched read-side critical section whose beginning + * preceded the call to synchronize_sched(). In addition, each CPU having + * an RCU read-side critical section that extends beyond the return from + * synchronize_sched() is guaranteed to have executed a full memory barrier + * after the beginning of synchronize_sched() and before the beginning of + * that RCU read-side critical section. Note that these guarantees include + * CPUs that are offline, idle, or executing in user mode, as well as CPUs + * that are executing in the kernel. + * + * Furthermore, if CPU A invoked synchronize_sched(), which returned + * to its caller on CPU B, then both CPU A and CPU B are guaranteed + * to have executed a full memory barrier during the execution of + * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but + * again only if the system has more than one CPU). + * + * This primitive provides the guarantees made by the (now removed) + * synchronize_kernel() API. In contrast, synchronize_rcu() only + * guarantees that rcu_read_lock() sections will have completed. + * In "classic RCU", these two guarantees happen to be one and + * the same, but can differ in realtime RCU implementations. + */ +void synchronize_sched(void) +{ + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_sched() in RCU-sched read-side critical section"); + if (rcu_blocking_is_gp()) + return; + if (rcu_gp_is_expedited()) + synchronize_sched_expedited(); + else + wait_rcu_gp(call_rcu_sched); +} +EXPORT_SYMBOL_GPL(synchronize_sched); + +/** + * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. + * + * Control will return to the caller some time after a full rcu_bh grace + * period has elapsed, in other words after all currently executing rcu_bh + * read-side critical sections have completed. RCU read-side critical + * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(), + * and may be nested. + * + * See the description of synchronize_sched() for more detailed information + * on memory ordering guarantees. + */ +void synchronize_rcu_bh(void) +{ + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section"); + if (rcu_blocking_is_gp()) + return; + if (rcu_gp_is_expedited()) + synchronize_rcu_bh_expedited(); + else + wait_rcu_gp(call_rcu_bh); +} +EXPORT_SYMBOL_GPL(synchronize_rcu_bh); + +/** + * get_state_synchronize_rcu - Snapshot current RCU state + * + * Returns a cookie that is used by a later call to cond_synchronize_rcu() + * to determine whether or not a full grace period has elapsed in the + * meantime. + */ +unsigned long get_state_synchronize_rcu(void) +{ + /* + * Any prior manipulation of RCU-protected data must happen + * before the load from ->gpnum. + */ + smp_mb(); /* ^^^ */ + + /* + * Make sure this load happens before the purportedly + * time-consuming work between get_state_synchronize_rcu() + * and cond_synchronize_rcu(). + */ + return smp_load_acquire(&rcu_state_p->gpnum); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); + +/** + * cond_synchronize_rcu - Conditionally wait for an RCU grace period + * + * @oldstate: return value from earlier call to get_state_synchronize_rcu() + * + * If a full RCU grace period has elapsed since the earlier call to + * get_state_synchronize_rcu(), just return. Otherwise, invoke + * synchronize_rcu() to wait for a full grace period. + * + * Yes, this function does not take counter wrap into account. But + * counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for one additional grace period should be just fine. + */ +void cond_synchronize_rcu(unsigned long oldstate) +{ + unsigned long newstate; + + /* + * Ensure that this load happens before any RCU-destructive + * actions the caller might carry out after we return. + */ + newstate = smp_load_acquire(&rcu_state_p->completed); + if (ULONG_CMP_GE(oldstate, newstate)) + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu); + +/** + * get_state_synchronize_sched - Snapshot current RCU-sched state + * + * Returns a cookie that is used by a later call to cond_synchronize_sched() + * to determine whether or not a full grace period has elapsed in the + * meantime. + */ +unsigned long get_state_synchronize_sched(void) +{ + /* + * Any prior manipulation of RCU-protected data must happen + * before the load from ->gpnum. + */ + smp_mb(); /* ^^^ */ + + /* + * Make sure this load happens before the purportedly + * time-consuming work between get_state_synchronize_sched() + * and cond_synchronize_sched(). + */ + return smp_load_acquire(&rcu_sched_state.gpnum); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_sched); + +/** + * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period + * + * @oldstate: return value from earlier call to get_state_synchronize_sched() + * + * If a full RCU-sched grace period has elapsed since the earlier call to + * get_state_synchronize_sched(), just return. Otherwise, invoke + * synchronize_sched() to wait for a full grace period. + * + * Yes, this function does not take counter wrap into account. But + * counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for one additional grace period should be just fine. + */ +void cond_synchronize_sched(unsigned long oldstate) +{ + unsigned long newstate; + + /* + * Ensure that this load happens before any RCU-destructive + * actions the caller might carry out after we return. + */ + newstate = smp_load_acquire(&rcu_sched_state.completed); + if (ULONG_CMP_GE(oldstate, newstate)) + synchronize_sched(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_sched); + +/* Adjust sequence number for start of update-side operation. */ +static void rcu_seq_start(unsigned long *sp) +{ + WRITE_ONCE(*sp, *sp + 1); + smp_mb(); /* Ensure update-side operation after counter increment. */ + WARN_ON_ONCE(!(*sp & 0x1)); +} + +/* Adjust sequence number for end of update-side operation. */ +static void rcu_seq_end(unsigned long *sp) +{ + smp_mb(); /* Ensure update-side operation before counter increment. */ + WRITE_ONCE(*sp, *sp + 1); + WARN_ON_ONCE(*sp & 0x1); +} + +/* Take a snapshot of the update side's sequence number. */ +static unsigned long rcu_seq_snap(unsigned long *sp) +{ + unsigned long s; + + smp_mb(); /* Caller's modifications seen first by other CPUs. */ + s = (READ_ONCE(*sp) + 3) & ~0x1; + smp_mb(); /* Above access must not bleed into critical section. */ + return s; +} + +/* + * Given a snapshot from rcu_seq_snap(), determine whether or not a + * full update-side operation has occurred. + */ +static bool rcu_seq_done(unsigned long *sp, unsigned long s) +{ + return ULONG_CMP_GE(READ_ONCE(*sp), s); +} + +/* Wrapper functions for expedited grace periods. */ +static void rcu_exp_gp_seq_start(struct rcu_state *rsp) +{ + rcu_seq_start(&rsp->expedited_sequence); +} +static void rcu_exp_gp_seq_end(struct rcu_state *rsp) +{ + rcu_seq_end(&rsp->expedited_sequence); + smp_mb(); /* Ensure that consecutive grace periods serialize. */ +} +static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp) +{ + return rcu_seq_snap(&rsp->expedited_sequence); +} +static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s) +{ + return rcu_seq_done(&rsp->expedited_sequence, s); +} + +/* + * Reset the ->expmaskinit values in the rcu_node tree to reflect any + * recent CPU-online activity. Note that these masks are not cleared + * when CPUs go offline, so they reflect the union of all CPUs that have + * ever been online. This means that this function normally takes its + * no-work-to-do fastpath. + */ +static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp) +{ + bool done; + unsigned long flags; + unsigned long mask; + unsigned long oldmask; + int ncpus = READ_ONCE(rsp->ncpus); + struct rcu_node *rnp; + struct rcu_node *rnp_up; + + /* If no new CPUs onlined since last time, nothing to do. */ + if (likely(ncpus == rsp->ncpus_snap)) + return; + rsp->ncpus_snap = ncpus; + + /* + * Each pass through the following loop propagates newly onlined + * CPUs for the current rcu_node structure up the rcu_node tree. + */ + rcu_for_each_leaf_node(rsp, rnp) { + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + if (rnp->expmaskinit == rnp->expmaskinitnext) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + continue; /* No new CPUs, nothing to do. */ + } + + /* Update this node's mask, track old value for propagation. */ + oldmask = rnp->expmaskinit; + rnp->expmaskinit = rnp->expmaskinitnext; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + + /* If was already nonzero, nothing to propagate. */ + if (oldmask) + continue; + + /* Propagate the new CPU up the tree. */ + mask = rnp->grpmask; + rnp_up = rnp->parent; + done = false; + while (rnp_up) { + raw_spin_lock_irqsave(&rnp_up->lock, flags); + smp_mb__after_unlock_lock(); + if (rnp_up->expmaskinit) + done = true; + rnp_up->expmaskinit |= mask; + raw_spin_unlock_irqrestore(&rnp_up->lock, flags); + if (done) + break; + mask = rnp_up->grpmask; + rnp_up = rnp_up->parent; + } + } +} + +/* + * Reset the ->expmask values in the rcu_node tree in preparation for + * a new expedited grace period. + */ +static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp) +{ + unsigned long flags; + struct rcu_node *rnp; + + sync_exp_reset_tree_hotplug(rsp); + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + WARN_ON_ONCE(rnp->expmask); + rnp->expmask = rnp->expmaskinit; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } +} + +/* + * Return non-zero if there is no RCU expedited grace period in progress + * for the specified rcu_node structure, in other words, if all CPUs and + * tasks covered by the specified rcu_node structure have done their bit + * for the current expedited grace period. Works only for preemptible + * RCU -- other RCU implementation use other means. + * + * Caller must hold the root rcu_node's exp_funnel_mutex. + */ +static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) +{ + return rnp->exp_tasks == NULL && + READ_ONCE(rnp->expmask) == 0; +} + +/* + * Report the exit from RCU read-side critical section for the last task + * that queued itself during or before the current expedited preemptible-RCU + * grace period. This event is reported either to the rcu_node structure on + * which the task was queued or to one of that rcu_node structure's ancestors, + * recursively up the tree. (Calm down, calm down, we do the recursion + * iteratively!) + * + * Caller must hold the root rcu_node's exp_funnel_mutex and the + * specified rcu_node structure's ->lock. + */ +static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, + bool wake, unsigned long flags) + __releases(rnp->lock) +{ + unsigned long mask; + + for (;;) { + if (!sync_rcu_preempt_exp_done(rnp)) { + if (!rnp->expmask) + rcu_initiate_boost(rnp, flags); + else + raw_spin_unlock_irqrestore(&rnp->lock, flags); + break; + } + if (rnp->parent == NULL) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (wake) { + smp_mb(); /* EGP done before wake_up(). */ + wake_up(&rsp->expedited_wq); + } + break; + } + mask = rnp->grpmask; + raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ + rnp = rnp->parent; + raw_spin_lock(&rnp->lock); /* irqs already disabled */ + smp_mb__after_unlock_lock(); + WARN_ON_ONCE(!(rnp->expmask & mask)); + rnp->expmask &= ~mask; + } +} + +/* + * Report expedited quiescent state for specified node. This is a + * lock-acquisition wrapper function for __rcu_report_exp_rnp(). + * + * Caller must hold the root rcu_node's exp_funnel_mutex. + */ +static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp, + struct rcu_node *rnp, bool wake) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + __rcu_report_exp_rnp(rsp, rnp, wake, flags); +} + +/* + * Report expedited quiescent state for multiple CPUs, all covered by the + * specified leaf rcu_node structure. Caller must hold the root + * rcu_node's exp_funnel_mutex. + */ +static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp, + unsigned long mask, bool wake) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + if (!(rnp->expmask & mask)) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + rnp->expmask &= ~mask; + __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */ +} + +/* + * Report expedited quiescent state for specified rcu_data (CPU). + * Caller must hold the root rcu_node's exp_funnel_mutex. + */ +static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp, + bool wake) +{ + rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake); +} + +/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */ +static bool sync_exp_work_done(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp, + atomic_long_t *stat, unsigned long s) +{ + if (rcu_exp_gp_seq_done(rsp, s)) { + if (rnp) + mutex_unlock(&rnp->exp_funnel_mutex); + else if (rdp) + mutex_unlock(&rdp->exp_funnel_mutex); + /* Ensure test happens before caller kfree(). */ + smp_mb__before_atomic(); /* ^^^ */ + atomic_long_inc(stat); + return true; + } + return false; +} + +/* + * Funnel-lock acquisition for expedited grace periods. Returns a + * pointer to the root rcu_node structure, or NULL if some other + * task did the expedited grace period for us. + */ +static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s) +{ + struct rcu_data *rdp; + struct rcu_node *rnp0; + struct rcu_node *rnp1 = NULL; + + /* + * First try directly acquiring the root lock in order to reduce + * latency in the common case where expedited grace periods are + * rare. We check mutex_is_locked() to avoid pathological levels of + * memory contention on ->exp_funnel_mutex in the heavy-load case. + */ + rnp0 = rcu_get_root(rsp); + if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) { + if (mutex_trylock(&rnp0->exp_funnel_mutex)) { + if (sync_exp_work_done(rsp, rnp0, NULL, + &rsp->expedited_workdone0, s)) + return NULL; + return rnp0; + } + } + + /* + * Each pass through the following loop works its way + * up the rcu_node tree, returning if others have done the + * work or otherwise falls through holding the root rnp's + * ->exp_funnel_mutex. The mapping from CPU to rcu_node structure + * can be inexact, as it is just promoting locality and is not + * strictly needed for correctness. + */ + rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id()); + if (sync_exp_work_done(rsp, NULL, NULL, &rsp->expedited_workdone1, s)) + return NULL; + mutex_lock(&rdp->exp_funnel_mutex); + rnp0 = rdp->mynode; + for (; rnp0 != NULL; rnp0 = rnp0->parent) { + if (sync_exp_work_done(rsp, rnp1, rdp, + &rsp->expedited_workdone2, s)) + return NULL; + mutex_lock(&rnp0->exp_funnel_mutex); + if (rnp1) + mutex_unlock(&rnp1->exp_funnel_mutex); + else + mutex_unlock(&rdp->exp_funnel_mutex); + rnp1 = rnp0; + } + if (sync_exp_work_done(rsp, rnp1, rdp, + &rsp->expedited_workdone3, s)) + return NULL; + return rnp1; +} + +/* Invoked on each online non-idle CPU for expedited quiescent state. */ +static void sync_sched_exp_handler(void *data) +{ + struct rcu_data *rdp; + struct rcu_node *rnp; + struct rcu_state *rsp = data; + + rdp = this_cpu_ptr(rsp->rda); + rnp = rdp->mynode; + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || + __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) + return; + __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true); + resched_cpu(smp_processor_id()); +} + +/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ +static void sync_sched_exp_online_cleanup(int cpu) +{ + struct rcu_data *rdp; + int ret; + struct rcu_node *rnp; + struct rcu_state *rsp = &rcu_sched_state; + + rdp = per_cpu_ptr(rsp->rda, cpu); + rnp = rdp->mynode; + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask)) + return; + ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0); + WARN_ON_ONCE(ret); +} + +/* + * Select the nodes that the upcoming expedited grace period needs + * to wait for. + */ +static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, + smp_call_func_t func) +{ + int cpu; + unsigned long flags; + unsigned long mask; + unsigned long mask_ofl_test; + unsigned long mask_ofl_ipi; + int ret; + struct rcu_node *rnp; + + sync_exp_reset_tree(rsp); + rcu_for_each_leaf_node(rsp, rnp) { + raw_spin_lock_irqsave(&rnp->lock, flags); + smp_mb__after_unlock_lock(); + + /* Each pass checks a CPU for identity, offline, and idle. */ + mask_ofl_test = 0; + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); + + if (raw_smp_processor_id() == cpu || + !(atomic_add_return(0, &rdtp->dynticks) & 0x1)) + mask_ofl_test |= rdp->grpmask; + } + mask_ofl_ipi = rnp->expmask & ~mask_ofl_test; + + /* + * Need to wait for any blocked tasks as well. Note that + * additional blocking tasks will also block the expedited + * GP until such time as the ->expmask bits are cleared. + */ + if (rcu_preempt_has_tasks(rnp)) + rnp->exp_tasks = rnp->blkd_tasks.next; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + + /* IPI the remaining CPUs for expedited quiescent state. */ + mask = 1; + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) { + if (!(mask_ofl_ipi & mask)) + continue; +retry_ipi: + ret = smp_call_function_single(cpu, func, rsp, 0); + if (!ret) { + mask_ofl_ipi &= ~mask; + } else { + /* Failed, raced with offline. */ + raw_spin_lock_irqsave(&rnp->lock, flags); + if (cpu_online(cpu) && + (rnp->expmask & mask)) { + raw_spin_unlock_irqrestore(&rnp->lock, + flags); + schedule_timeout_uninterruptible(1); + if (cpu_online(cpu) && + (rnp->expmask & mask)) + goto retry_ipi; + raw_spin_lock_irqsave(&rnp->lock, + flags); + } + if (!(rnp->expmask & mask)) + mask_ofl_ipi &= ~mask; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } + } + /* Report quiescent states for those that went offline. */ + mask_ofl_test |= mask_ofl_ipi; + if (mask_ofl_test) + rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false); + } +} + +static void synchronize_sched_expedited_wait(struct rcu_state *rsp) +{ + int cpu; + unsigned long jiffies_stall; + unsigned long jiffies_start; + unsigned long mask; + struct rcu_node *rnp; + struct rcu_node *rnp_root = rcu_get_root(rsp); + int ret; + + jiffies_stall = rcu_jiffies_till_stall_check(); + jiffies_start = jiffies; + + for (;;) { + ret = wait_event_interruptible_timeout( + rsp->expedited_wq, + sync_rcu_preempt_exp_done(rnp_root), + jiffies_stall); + if (ret > 0) + return; + if (ret < 0) { + /* Hit a signal, disable CPU stall warnings. */ + wait_event(rsp->expedited_wq, + sync_rcu_preempt_exp_done(rnp_root)); + return; + } + pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", + rsp->name); + rcu_for_each_leaf_node(rsp, rnp) { + (void)rcu_print_task_exp_stall(rnp); + mask = 1; + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) { + struct rcu_data *rdp; + + if (!(rnp->expmask & mask)) + continue; + rdp = per_cpu_ptr(rsp->rda, cpu); + pr_cont(" %d-%c%c%c", cpu, + "O."[!!cpu_online(cpu)], + "o."[!!(rdp->grpmask & rnp->expmaskinit)], + "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]); + } + mask <<= 1; + } + pr_cont(" } %lu jiffies s: %lu\n", + jiffies - jiffies_start, rsp->expedited_sequence); + rcu_for_each_leaf_node(rsp, rnp) { + mask = 1; + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) { + if (!(rnp->expmask & mask)) + continue; + dump_cpu_task(cpu); + } + } + jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3; + } +} + +/** + * synchronize_sched_expedited - Brute-force RCU-sched grace period + * + * Wait for an RCU-sched grace period to elapse, but use a "big hammer" + * approach to force the grace period to end quickly. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. In fact, + * if you are using synchronize_sched_expedited() in a loop, please + * restructure your code to batch your updates, and then use a single + * synchronize_sched() instead. + * + * This implementation can be thought of as an application of sequence + * locking to expedited grace periods, but using the sequence counter to + * determine when someone else has already done the work instead of for + * retrying readers. + */ +void synchronize_sched_expedited(void) +{ + unsigned long s; + struct rcu_node *rnp; + struct rcu_state *rsp = &rcu_sched_state; + + /* Take a snapshot of the sequence number. */ + s = rcu_exp_gp_seq_snap(rsp); + + rnp = exp_funnel_lock(rsp, s); + if (rnp == NULL) + return; /* Someone else did our work for us. */ + + rcu_exp_gp_seq_start(rsp); + sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler); + synchronize_sched_expedited_wait(rsp); + + rcu_exp_gp_seq_end(rsp); + mutex_unlock(&rnp->exp_funnel_mutex); +} +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); + +/* + * Check to see if there is any immediate RCU-related work to be done + * by the current CPU, for the specified type of RCU, returning 1 if so. + * The checks are in order of increasing expense: checks that can be + * carried out against CPU-local state are performed first. However, + * we must check for CPU stalls first, else we might not get a chance. + */ +static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) +{ + struct rcu_node *rnp = rdp->mynode; + + rdp->n_rcu_pending++; + + /* Check for CPU stalls, if enabled. */ + check_cpu_stall(rsp, rdp); + + /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */ + if (rcu_nohz_full_cpu(rsp)) + return 0; + + /* Is the RCU core waiting for a quiescent state from this CPU? */ + if (rcu_scheduler_fully_active && + rdp->core_needs_qs && rdp->cpu_no_qs.b.norm && + rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) { + rdp->n_rp_core_needs_qs++; + } else if (rdp->core_needs_qs && + (!rdp->cpu_no_qs.b.norm || + rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) { + rdp->n_rp_report_qs++; + return 1; + } + + /* Does this CPU have callbacks ready to invoke? */ + if (cpu_has_callbacks_ready_to_invoke(rdp)) { + rdp->n_rp_cb_ready++; + return 1; + } + + /* Has RCU gone idle with this CPU needing another grace period? */ + if (cpu_needs_another_gp(rsp, rdp)) { + rdp->n_rp_cpu_needs_gp++; + return 1; + } + + /* Has another RCU grace period completed? */ + if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */ + rdp->n_rp_gp_completed++; + return 1; + } + + /* Has a new RCU grace period started? */ + if (READ_ONCE(rnp->gpnum) != rdp->gpnum || + unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */ + rdp->n_rp_gp_started++; + return 1; + } + + /* Does this CPU need a deferred NOCB wakeup? */ + if (rcu_nocb_need_deferred_wakeup(rdp)) { + rdp->n_rp_nocb_defer_wakeup++; + return 1; + } + + /* nothing to do */ + rdp->n_rp_need_nothing++; + return 0; +} + +/* + * Check to see if there is any immediate RCU-related work to be done + * by the current CPU, returning 1 if so. This function is part of the + * RCU implementation; it is -not- an exported member of the RCU API. + */ +static int rcu_pending(void) +{ + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) + if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda))) + return 1; + return 0; +} + +/* + * Return true if the specified CPU has any callback. If all_lazy is + * non-NULL, store an indication of whether all callbacks are lazy. + * (If there are no callbacks, all of them are deemed to be lazy.) + */ +static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy) +{ + bool al = true; + bool hc = false; + struct rcu_data *rdp; + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) { + rdp = this_cpu_ptr(rsp->rda); + if (!rdp->nxtlist) + continue; + hc = true; + if (rdp->qlen != rdp->qlen_lazy || !all_lazy) { + al = false; + break; + } + } + if (all_lazy) + *all_lazy = al; + return hc; +} + +/* + * Helper function for _rcu_barrier() tracing. If tracing is disabled, + * the compiler is expected to optimize this away. + */ +static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s, + int cpu, unsigned long done) +{ + trace_rcu_barrier(rsp->name, s, cpu, + atomic_read(&rsp->barrier_cpu_count), done); +} + +/* + * RCU callback function for _rcu_barrier(). If we are last, wake + * up the task executing _rcu_barrier(). + */ +static void rcu_barrier_callback(struct rcu_head *rhp) +{ + struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head); + struct rcu_state *rsp = rdp->rsp; + + if (atomic_dec_and_test(&rsp->barrier_cpu_count)) { + _rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence); + complete(&rsp->barrier_completion); + } else { + _rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence); + } +} + +/* + * Called with preemption disabled, and from cross-cpu IRQ context. + */ +static void rcu_barrier_func(void *type) +{ + struct rcu_state *rsp = type; + struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); + + _rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence); + atomic_inc(&rsp->barrier_cpu_count); + rsp->call(&rdp->barrier_head, rcu_barrier_callback); +} + +/* + * Orchestrate the specified type of RCU barrier, waiting for all + * RCU callbacks of the specified type to complete. + */ +static void _rcu_barrier(struct rcu_state *rsp) +{ + int cpu; + struct rcu_data *rdp; + unsigned long s = rcu_seq_snap(&rsp->barrier_sequence); + + _rcu_barrier_trace(rsp, "Begin", -1, s); + + /* Take mutex to serialize concurrent rcu_barrier() requests. */ + mutex_lock(&rsp->barrier_mutex); + + /* Did someone else do our work for us? */ + if (rcu_seq_done(&rsp->barrier_sequence, s)) { + _rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence); + smp_mb(); /* caller's subsequent code after above check. */ + mutex_unlock(&rsp->barrier_mutex); + return; + } + + /* Mark the start of the barrier operation. */ + rcu_seq_start(&rsp->barrier_sequence); + _rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence); + + /* + * Initialize the count to one rather than to zero in order to + * avoid a too-soon return to zero in case of a short grace period + * (or preemption of this task). Exclude CPU-hotplug operations + * to ensure that no offline CPU has callbacks queued. + */ + init_completion(&rsp->barrier_completion); + atomic_set(&rsp->barrier_cpu_count, 1); + get_online_cpus(); + + /* + * Force each CPU with callbacks to register a new callback. + * When that callback is invoked, we will know that all of the + * corresponding CPU's preceding callbacks have been invoked. + */ + for_each_possible_cpu(cpu) { + if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu)) + continue; + rdp = per_cpu_ptr(rsp->rda, cpu); + if (rcu_is_nocb_cpu(cpu)) { + if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) { + _rcu_barrier_trace(rsp, "OfflineNoCB", cpu, + rsp->barrier_sequence); + } else { + _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, + rsp->barrier_sequence); + smp_mb__before_atomic(); + atomic_inc(&rsp->barrier_cpu_count); + __call_rcu(&rdp->barrier_head, + rcu_barrier_callback, rsp, cpu, 0); + } + } else if (READ_ONCE(rdp->qlen)) { + _rcu_barrier_trace(rsp, "OnlineQ", cpu, + rsp->barrier_sequence); + smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); + } else { + _rcu_barrier_trace(rsp, "OnlineNQ", cpu, + rsp->barrier_sequence); + } + } + put_online_cpus(); + + /* + * Now that we have an rcu_barrier_callback() callback on each + * CPU, and thus each counted, remove the initial count. + */ + if (atomic_dec_and_test(&rsp->barrier_cpu_count)) + complete(&rsp->barrier_completion); + + /* Wait for all rcu_barrier_callback() callbacks to be invoked. */ + wait_for_completion(&rsp->barrier_completion); + + /* Mark the end of the barrier operation. */ + _rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence); + rcu_seq_end(&rsp->barrier_sequence); + + /* Other rcu_barrier() invocations can now safely proceed. */ + mutex_unlock(&rsp->barrier_mutex); +} + +/** + * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. + */ +void rcu_barrier_bh(void) +{ + _rcu_barrier(&rcu_bh_state); +} +EXPORT_SYMBOL_GPL(rcu_barrier_bh); + +/** + * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. + */ +void rcu_barrier_sched(void) +{ + _rcu_barrier(&rcu_sched_state); +} +EXPORT_SYMBOL_GPL(rcu_barrier_sched); + +/* + * Propagate ->qsinitmask bits up the rcu_node tree to account for the + * first CPU in a given leaf rcu_node structure coming online. The caller + * must hold the corresponding leaf rcu_node ->lock with interrrupts + * disabled. + */ +static void rcu_init_new_rnp(struct rcu_node *rnp_leaf) +{ + long mask; + struct rcu_node *rnp = rnp_leaf; + + for (;;) { + mask = rnp->grpmask; + rnp = rnp->parent; + if (rnp == NULL) + return; + raw_spin_lock(&rnp->lock); /* Interrupts already disabled. */ + rnp->qsmaskinit |= mask; + raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */ + } +} + +/* + * Do boot-time initialization of a CPU's per-CPU RCU data. + */ +static void __init +rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) +{ + unsigned long flags; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_node *rnp = rcu_get_root(rsp); + + /* Set up local state, ensuring consistent view of global state. */ + raw_spin_lock_irqsave(&rnp->lock, flags); + rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo); + rdp->dynticks = &per_cpu(rcu_dynticks, cpu); + WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE); + WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1); + rdp->cpu = cpu; + rdp->rsp = rsp; + mutex_init(&rdp->exp_funnel_mutex); + rcu_boot_init_nocb_percpu_data(rdp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); +} + +/* + * Initialize a CPU's per-CPU RCU data. Note that only one online or + * offline event can be happening at a given time. Note also that we + * can accept some slop in the rsp->completed access due to the fact + * that this CPU cannot possibly have any RCU callbacks in flight yet. + */ +static void +rcu_init_percpu_data(int cpu, struct rcu_state *rsp) +{ + unsigned long flags; + unsigned long mask; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_node *rnp = rcu_get_root(rsp); + + /* Set up local state, ensuring consistent view of global state. */ + raw_spin_lock_irqsave(&rnp->lock, flags); + rdp->qlen_last_fqs_check = 0; + rdp->n_force_qs_snap = rsp->n_force_qs; + rdp->blimit = blimit; + if (!rdp->nxtlist) + init_callback_list(rdp); /* Re-enable callbacks on this CPU. */ + rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; + rcu_sysidle_init_percpu_data(rdp->dynticks); + atomic_set(&rdp->dynticks->dynticks, + (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + + /* + * Add CPU to leaf rcu_node pending-online bitmask. Any needed + * propagation up the rcu_node tree will happen at the beginning + * of the next grace period. + */ + rnp = rdp->mynode; + mask = rdp->grpmask; + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + smp_mb__after_unlock_lock(); + rnp->qsmaskinitnext |= mask; + rnp->expmaskinitnext |= mask; + if (!rdp->beenonline) + WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1); + rdp->beenonline = true; /* We have now been online. */ + rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */ + rdp->completed = rnp->completed; + rdp->cpu_no_qs.b.norm = true; + rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu); + rdp->core_needs_qs = false; + trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl")); + raw_spin_unlock_irqrestore(&rnp->lock, flags); +} + +static void rcu_prepare_cpu(int cpu) +{ + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) + rcu_init_percpu_data(cpu, rsp); +} + +/* + * Handle CPU online/offline notification events. + */ +int rcu_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + long cpu = (long)hcpu; + struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); + struct rcu_node *rnp = rdp->mynode; + struct rcu_state *rsp; + + switch (action) { + case CPU_UP_PREPARE: + case CPU_UP_PREPARE_FROZEN: + rcu_prepare_cpu(cpu); + rcu_prepare_kthreads(cpu); + rcu_spawn_all_nocb_kthreads(cpu); + break; + case CPU_ONLINE: + case CPU_DOWN_FAILED: + sync_sched_exp_online_cleanup(cpu); + rcu_boost_kthread_setaffinity(rnp, -1); + break; + case CPU_DOWN_PREPARE: + rcu_boost_kthread_setaffinity(rnp, cpu); + break; + case CPU_DYING: + case CPU_DYING_FROZEN: + for_each_rcu_flavor(rsp) + rcu_cleanup_dying_cpu(rsp); + break; + case CPU_DYING_IDLE: + /* QS for any half-done expedited RCU-sched GP. */ + preempt_disable(); + rcu_report_exp_rdp(&rcu_sched_state, + this_cpu_ptr(rcu_sched_state.rda), true); + preempt_enable(); + + for_each_rcu_flavor(rsp) { + rcu_cleanup_dying_idle_cpu(cpu, rsp); + } + break; + case CPU_DEAD: + case CPU_DEAD_FROZEN: + case CPU_UP_CANCELED: + case CPU_UP_CANCELED_FROZEN: + for_each_rcu_flavor(rsp) { + rcu_cleanup_dead_cpu(cpu, rsp); + do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu)); + } + break; + default: + break; + } + return NOTIFY_OK; +} + +static int rcu_pm_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + switch (action) { + case PM_HIBERNATION_PREPARE: + case PM_SUSPEND_PREPARE: + if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ + rcu_expedite_gp(); + break; + case PM_POST_HIBERNATION: + case PM_POST_SUSPEND: + if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ + rcu_unexpedite_gp(); + break; + default: + break; + } + return NOTIFY_OK; +} + +/* + * Spawn the kthreads that handle each RCU flavor's grace periods. + */ +static int __init rcu_spawn_gp_kthread(void) +{ + unsigned long flags; + int kthread_prio_in = kthread_prio; + struct rcu_node *rnp; + struct rcu_state *rsp; + struct sched_param sp; + struct task_struct *t; + + /* Force priority into range. */ + if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1) + kthread_prio = 1; + else if (kthread_prio < 0) + kthread_prio = 0; + else if (kthread_prio > 99) + kthread_prio = 99; + if (kthread_prio != kthread_prio_in) + pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n", + kthread_prio, kthread_prio_in); + + rcu_scheduler_fully_active = 1; + for_each_rcu_flavor(rsp) { + t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name); + BUG_ON(IS_ERR(t)); + rnp = rcu_get_root(rsp); + raw_spin_lock_irqsave(&rnp->lock, flags); + rsp->gp_kthread = t; + if (kthread_prio) { + sp.sched_priority = kthread_prio; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + } + wake_up_process(t); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } + rcu_spawn_nocb_kthreads(); + rcu_spawn_boost_kthreads(); + return 0; +} +early_initcall(rcu_spawn_gp_kthread); + +/* + * This function is invoked towards the end of the scheduler's initialization + * process. Before this is called, the idle task might contain + * RCU read-side critical sections (during which time, this idle + * task is booting the system). After this function is called, the + * idle tasks are prohibited from containing RCU read-side critical + * sections. This function also enables RCU lockdep checking. + */ +void rcu_scheduler_starting(void) +{ + WARN_ON(num_online_cpus() != 1); + WARN_ON(nr_context_switches() > 0); + rcu_scheduler_active = 1; +} + +/* + * Compute the per-level fanout, either using the exact fanout specified + * or balancing the tree, depending on the rcu_fanout_exact boot parameter. + */ +static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt) +{ + int i; + + if (rcu_fanout_exact) { + levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf; + for (i = rcu_num_lvls - 2; i >= 0; i--) + levelspread[i] = RCU_FANOUT; + } else { + int ccur; + int cprv; + + cprv = nr_cpu_ids; + for (i = rcu_num_lvls - 1; i >= 0; i--) { + ccur = levelcnt[i]; + levelspread[i] = (cprv + ccur - 1) / ccur; + cprv = ccur; + } + } +} + +/* + * Helper function for rcu_init() that initializes one rcu_state structure. + */ +static void __init rcu_init_one(struct rcu_state *rsp, + struct rcu_data __percpu *rda) +{ + static const char * const buf[] = RCU_NODE_NAME_INIT; + static const char * const fqs[] = RCU_FQS_NAME_INIT; + static const char * const exp[] = RCU_EXP_NAME_INIT; + static u8 fl_mask = 0x1; + + int levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */ + int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */ + int cpustride = 1; + int i; + int j; + struct rcu_node *rnp; + + BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */ + + /* Silence gcc 4.8 false positive about array index out of range. */ + if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS) + panic("rcu_init_one: rcu_num_lvls out of range"); + + /* Initialize the level-tracking arrays. */ + + for (i = 0; i < rcu_num_lvls; i++) + levelcnt[i] = num_rcu_lvl[i]; + for (i = 1; i < rcu_num_lvls; i++) + rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1]; + rcu_init_levelspread(levelspread, levelcnt); + rsp->flavor_mask = fl_mask; + fl_mask <<= 1; + + /* Initialize the elements themselves, starting from the leaves. */ + + for (i = rcu_num_lvls - 1; i >= 0; i--) { + cpustride *= levelspread[i]; + rnp = rsp->level[i]; + for (j = 0; j < levelcnt[i]; j++, rnp++) { + raw_spin_lock_init(&rnp->lock); + lockdep_set_class_and_name(&rnp->lock, + &rcu_node_class[i], buf[i]); + raw_spin_lock_init(&rnp->fqslock); + lockdep_set_class_and_name(&rnp->fqslock, + &rcu_fqs_class[i], fqs[i]); + rnp->gpnum = rsp->gpnum; + rnp->completed = rsp->completed; + rnp->qsmask = 0; + rnp->qsmaskinit = 0; + rnp->grplo = j * cpustride; + rnp->grphi = (j + 1) * cpustride - 1; + if (rnp->grphi >= nr_cpu_ids) + rnp->grphi = nr_cpu_ids - 1; + if (i == 0) { + rnp->grpnum = 0; + rnp->grpmask = 0; + rnp->parent = NULL; + } else { + rnp->grpnum = j % levelspread[i - 1]; + rnp->grpmask = 1UL << rnp->grpnum; + rnp->parent = rsp->level[i - 1] + + j / levelspread[i - 1]; + } + rnp->level = i; + INIT_LIST_HEAD(&rnp->blkd_tasks); + rcu_init_one_nocb(rnp); + mutex_init(&rnp->exp_funnel_mutex); + lockdep_set_class_and_name(&rnp->exp_funnel_mutex, + &rcu_exp_class[i], exp[i]); + } + } + + init_waitqueue_head(&rsp->gp_wq); + init_waitqueue_head(&rsp->expedited_wq); + rnp = rsp->level[rcu_num_lvls - 1]; + for_each_possible_cpu(i) { + while (i > rnp->grphi) + rnp++; + per_cpu_ptr(rsp->rda, i)->mynode = rnp; + rcu_boot_init_percpu_data(i, rsp); + } + list_add(&rsp->flavors, &rcu_struct_flavors); +} + +/* + * Compute the rcu_node tree geometry from kernel parameters. This cannot + * replace the definitions in tree.h because those are needed to size + * the ->node array in the rcu_state structure. + */ +static void __init rcu_init_geometry(void) +{ + ulong d; + int i; + int rcu_capacity[RCU_NUM_LVLS]; + + /* + * Initialize any unspecified boot parameters. + * The default values of jiffies_till_first_fqs and + * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS + * value, which is a function of HZ, then adding one for each + * RCU_JIFFIES_FQS_DIV CPUs that might be on the system. + */ + d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; + if (jiffies_till_first_fqs == ULONG_MAX) + jiffies_till_first_fqs = d; + if (jiffies_till_next_fqs == ULONG_MAX) + jiffies_till_next_fqs = d; + + /* If the compile-time values are accurate, just leave. */ + if (rcu_fanout_leaf == RCU_FANOUT_LEAF && + nr_cpu_ids == NR_CPUS) + return; + pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n", + rcu_fanout_leaf, nr_cpu_ids); + + /* + * The boot-time rcu_fanout_leaf parameter must be at least two + * and cannot exceed the number of bits in the rcu_node masks. + * Complain and fall back to the compile-time values if this + * limit is exceeded. + */ + if (rcu_fanout_leaf < 2 || + rcu_fanout_leaf > sizeof(unsigned long) * 8) { + rcu_fanout_leaf = RCU_FANOUT_LEAF; + WARN_ON(1); + return; + } + + /* + * Compute number of nodes that can be handled an rcu_node tree + * with the given number of levels. + */ + rcu_capacity[0] = rcu_fanout_leaf; + for (i = 1; i < RCU_NUM_LVLS; i++) + rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT; + + /* + * The tree must be able to accommodate the configured number of CPUs. + * If this limit is exceeded, fall back to the compile-time values. + */ + if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) { + rcu_fanout_leaf = RCU_FANOUT_LEAF; + WARN_ON(1); + return; + } + + /* Calculate the number of levels in the tree. */ + for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) { + } + rcu_num_lvls = i + 1; + + /* Calculate the number of rcu_nodes at each level of the tree. */ + for (i = 0; i < rcu_num_lvls; i++) { + int cap = rcu_capacity[(rcu_num_lvls - 1) - i]; + num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap); + } + + /* Calculate the total number of rcu_node structures. */ + rcu_num_nodes = 0; + for (i = 0; i < rcu_num_lvls; i++) + rcu_num_nodes += num_rcu_lvl[i]; +} + +/* + * Dump out the structure of the rcu_node combining tree associated + * with the rcu_state structure referenced by rsp. + */ +static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp) +{ + int level = 0; + struct rcu_node *rnp; + + pr_info("rcu_node tree layout dump\n"); + pr_info(" "); + rcu_for_each_node_breadth_first(rsp, rnp) { + if (rnp->level != level) { + pr_cont("\n"); + pr_info(" "); + level = rnp->level; + } + pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum); + } + pr_cont("\n"); +} + +void __init rcu_init(void) +{ + int cpu; + + rcu_early_boot_tests(); + + rcu_bootup_announce(); + rcu_init_geometry(); + rcu_init_one(&rcu_bh_state, &rcu_bh_data); + rcu_init_one(&rcu_sched_state, &rcu_sched_data); + if (dump_tree) + rcu_dump_rcu_node_tree(&rcu_sched_state); + __rcu_init_preempt(); + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); + + /* + * We don't need protection against CPU-hotplug here because + * this is called early in boot, before either interrupts + * or the scheduler are operational. + */ + cpu_notifier(rcu_cpu_notify, 0); + pm_notifier(rcu_pm_notify, 0); + for_each_online_cpu(cpu) + rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu); +} + +#include "tree_plugin.h" |