diff options
| author | Junjie Wu <junjiew@codeaurora.org> | 2015-03-20 14:41:50 -0700 |
|---|---|---|
| committer | David Keitel <dkeitel@codeaurora.org> | 2016-03-23 20:04:16 -0700 |
| commit | f0da7256374da9ab055d1d85cdf0adcb47f9190e (patch) | |
| tree | cb440554fd8ee775a49a48e8dda3c3a41bc4ea74 /drivers/devfreq | |
| parent | cd77a0069f357ceaab9d77410b1b6bbed54363f1 (diff) | |
PM / devfreq: governor_cpufreq: Rewrite locking to avoid deadlocks
A devfreq governor store in parallel with a cpu freq update can cause
deadlock as shown below.
Assume current devfreq governor is cpufreq, and user tries to change
to some other governor.
Write to sysfs store_governor | cpufreq driver updating cpu freq
------------------------------- | -----------------------------------
echo bw_hwmon > governor |
| takes rcu_read_lock and calls all
| cpufreq transition callbacks for
| PRECHANGE or POSTCHANGE
|
GOV_STOP on governor_cpufreq. |
unregister_cpufreq() accquires |
state_lock mutex. |
| try to accquire same state_lock in
| cpufreq_trans_notifier(). Blocked.
unregister from cpufreq |
transition notifier and wait for|
all rcu_readers to finish. |
Deadlock
A similar deadlock can happen with governor change and policy notifier
callbacks.
The state_lock currently protects multiple unrelated critical
sections: registering/unregistering of cpufreq notifiers, read/writing
the device list, and tracking the cpu states and updating device
frequencies. There is no need for register/unregister of the cpufreq
notifiers to be mutually excluded against the other critical sections
using the same lock.
Split state_lock into two locks to protect the register/unregister of
cpufreq notifiers from the rest of the critical sections.
Change-Id: Id06d326748a5cb0c84c4787da5d0910f44eb5c3c
Signed-off-by: Pan Fang <fangpan@codeaurora.org>
Signed-off-by: Arun KS <arunks@codeaurora.org>
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
Suggested-by: Saravana Kannan <skannan@codeaurora.org>
Diffstat (limited to 'drivers/devfreq')
| -rw-r--r-- | drivers/devfreq/governor_cpufreq.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/drivers/devfreq/governor_cpufreq.c b/drivers/devfreq/governor_cpufreq.c index 01a6003cc391..fc4da03201f2 100644 --- a/drivers/devfreq/governor_cpufreq.c +++ b/drivers/devfreq/governor_cpufreq.c @@ -1,5 +1,5 @@ /* - * Copyright (c) 2014, The Linux Foundation. All rights reserved. + * Copyright (c) 2014-2015, The Linux Foundation. All rights reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 and @@ -53,6 +53,7 @@ struct devfreq_node { }; static LIST_HEAD(devfreq_list); static DEFINE_MUTEX(state_lock); +static DEFINE_MUTEX(cpufreq_reg_lock); #define show_attr(name) \ static ssize_t show_##name(struct device *dev, \ @@ -240,7 +241,7 @@ static int register_cpufreq(void) unsigned int cpu; struct cpufreq_policy *policy; - mutex_lock(&state_lock); + mutex_lock(&cpufreq_reg_lock); if (cpufreq_cnt) goto cnt_not_zero; @@ -271,7 +272,7 @@ out: cnt_not_zero: if (!ret) cpufreq_cnt++; - mutex_unlock(&state_lock); + mutex_unlock(&cpufreq_reg_lock); return ret; } @@ -280,7 +281,7 @@ static int unregister_cpufreq(void) int ret = 0; int cpu; - mutex_lock(&state_lock); + mutex_lock(&cpufreq_reg_lock); if (cpufreq_cnt > 1) goto out; @@ -300,7 +301,7 @@ static int unregister_cpufreq(void) out: cpufreq_cnt--; - mutex_unlock(&state_lock); + mutex_unlock(&cpufreq_reg_lock); return ret; } |