Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:

 - Continued initialization/Kconfig updates: hide most Kconfig options
   from unsuspecting users.

   There's now a single high level configuration option:

        *
        * RCU Subsystem
        *
        Make expert-level adjustments to RCU configuration (RCU_EXPERT) [N/y/?] (NEW)

   Which if answered in the negative, leaves us with a single
   interactive configuration option:

        Offload RCU callback processing from boot-selected CPUs (RCU_NOCB_CPU) [N/y/?] (NEW)

   All the rest of the RCU options are configured automatically.  Later
   on we'll remove this single leftover configuration option as well.

 - Remove all uses of RCU-protected array indexes: replace the
   rcu_[access|dereference]_index_check() APIs with READ_ONCE() and
   rcu_lockdep_assert()

 - RCU CPU-hotplug cleanups

 - Updates to Tiny RCU: a race fix and further code shrinkage.

 - RCU torture-testing updates: fixes, speedups, cleanups and
   documentation updates.

 - Miscellaneous fixes

 - Documentation updates

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
  rcutorture: Allow repetition factors in Kconfig-fragment lists
  rcutorture: Display "make oldconfig" errors
  rcutorture: Update TREE_RCU-kconfig.txt
  rcutorture: Make rcutorture scripts force RCU_EXPERT
  rcutorture: Update configuration fragments for rcutree.rcu_fanout_exact
  rcutorture: TASKS_RCU set directly, so don't explicitly set it
  rcutorture: Test SRCU cleanup code path
  rcutorture: Replace barriers with smp_store_release() and smp_load_acquire()
  locktorture: Change longdelay_us to longdelay_ms
  rcutorture: Allow negative values of nreaders to oversubscribe
  rcutorture: Exchange TREE03 and TREE08 NR_CPUS, speed up CPU hotplug
  rcutorture: Exchange TREE03 and TREE04 geometries
  locktorture: fix deadlock in 'rw_lock_irq' type
  rcu: Correctly handle non-empty Tiny RCU callback list with none ready
  rcutorture: Test both RCU-sched and RCU-bh for Tiny RCU
  rcu: Further shrink Tiny RCU by making empty functions static inlines
  rcu: Conditionally compile RCU's eqs warnings
  rcu: Remove prompt for RCU implementation
  rcu: Make RCU able to tolerate undefined CONFIG_RCU_KTHREAD_PRIO
  rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT_LEAF
  ...

1 files changed, 5 insertions, 33 deletions

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 069742d61c68..591af0cb7b9f 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -49,39 +49,6 @@ static void __call_rcu(struct rcu_head *head,
 
 #include "tiny_plugin.h"
 
-/*
- * Enter idle, which is an extended quiescent state if we have fully
- * entered that mode.
- */
-void rcu_idle_enter(void)
-{
-}
-EXPORT_SYMBOL_GPL(rcu_idle_enter);
-
-/*
- * Exit an interrupt handler towards idle.
- */
-void rcu_irq_exit(void)
-{
-}
-EXPORT_SYMBOL_GPL(rcu_irq_exit);
-
-/*
- * Exit idle, so that we are no longer in an extended quiescent state.
- */
-void rcu_idle_exit(void)
-{
-}
-EXPORT_SYMBOL_GPL(rcu_idle_exit);
-
-/*
- * Enter an interrupt handler, moving away from idle.
- */
-void rcu_irq_enter(void)
-{
-}
-EXPORT_SYMBOL_GPL(rcu_irq_enter);
-
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 
 /*
@@ -170,6 +137,11 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
+	if (rcp->donetail == &rcp->rcucblist) {
+		/* No callbacks ready, so just leave. */
+		local_irq_restore(flags);
+		return;
+	}
 	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 	list = rcp->rcucblist;
 	rcp->rcucblist = *rcp->donetail;