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cpufreq: interactive: fix racy timer stopping

Browse source 
When stopping the governor, del_timer_sync() can race against an
invocation of the idle notifier callback, which has the potential
to reactivate the timer.

To fix this issue, a read-write semaphore is used. Multiple readers are
allowed as long as pcpu->governor_enabled is true.  However it can be
moved to false only after taking a write semaphore which would wait for
any on-going asynchronous activities to complete and prevent any more of
those activities to be initiated.

[toddpoynor@google.com: cosmetic and commit text changes]
Change-Id: Ib51165a735d73dcf964a06754c48bdc1913e13d0
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
This commit is contained in:
Todd Poynor 2012-12-18 17:50:44 -08:00 committed by Arve Hjønnevåg
parent f5e5ad4292
commit beb55c19d5
1 changed files with 28 additions and 10 deletions
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38
drivers/cpufreq/cpufreq_interactive.c
View file

@ -21,7 +21,7 @@
#include <linux/cpufreq.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/mutex.h>
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/tick.h>
@ -29,7 +29,6 @@
#include <linux/timer.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm/cputime.h>
@ -52,6 +51,7 @@ struct cpufreq_interactive_cpuinfo {
unsigned int floor_freq;
u64 floor_validate_time;
u64 hispeed_validate_time;
struct rw_semaphore enable_sem;
int governor_enabled;
};
@ -279,8 +279,8 @@ static void cpufreq_interactive_timer(unsigned long data)
unsigned long flags;
bool boosted;
smp_rmb();
if (!down_read_trylock(&pcpu->enable_sem))
return;
if (!pcpu->governor_enabled)
goto exit;
@ -387,6 +387,7 @@ rearm:
cpufreq_interactive_timer_resched(pcpu);
exit:
up_read(&pcpu->enable_sem);
return;
}
@ -396,8 +397,12 @@ static void cpufreq_interactive_idle_start(void)
&per_cpu(cpuinfo, smp_processor_id());
int pending;
if (!pcpu->governor_enabled)
if (!down_read_trylock(&pcpu->enable_sem))
return;
if (!pcpu->governor_enabled) {
up_read(&pcpu->enable_sem);
return;
}
pending = timer_pending(&pcpu->cpu_timer);
@ -414,6 +419,7 @@ static void cpufreq_interactive_idle_start(void)
cpufreq_interactive_timer_resched(pcpu);
}
up_read(&pcpu->enable_sem);
}
static void cpufreq_interactive_idle_end(void)
@ -421,8 +427,12 @@ static void cpufreq_interactive_idle_end(void)
struct cpufreq_interactive_cpuinfo *pcpu =
&per_cpu(cpuinfo, smp_processor_id());
if (!pcpu->governor_enabled)
if (!down_read_trylock(&pcpu->enable_sem))
return;
if (!pcpu->governor_enabled) {
up_read(&pcpu->enable_sem);
return;
}
/* Arm the timer for 1-2 ticks later if not already. */
if (!timer_pending(&pcpu->cpu_timer)) {
@ -432,6 +442,8 @@ static void cpufreq_interactive_idle_end(void)
del_timer(&pcpu->cpu_slack_timer);
cpufreq_interactive_timer(smp_processor_id());
}
up_read(&pcpu->enable_sem);
}
static int cpufreq_interactive_speedchange_task(void *data)
@ -466,10 +478,12 @@ static int cpufreq_interactive_speedchange_task(void *data)
unsigned int max_freq = 0;
pcpu = &per_cpu(cpuinfo, cpu);
smp_rmb();
if (!pcpu->governor_enabled)
if (!down_read_trylock(&pcpu->enable_sem))
continue;
if (!pcpu->governor_enabled) {
up_read(&pcpu->enable_sem);
continue;
}
for_each_cpu(j, pcpu->policy->cpus) {
struct cpufreq_interactive_cpuinfo *pjcpu =
@ -486,6 +500,8 @@ static int cpufreq_interactive_speedchange_task(void *data)
trace_cpufreq_interactive_setspeed(cpu,
pcpu->target_freq,
pcpu->policy->cur);
up_read(&pcpu->enable_sem);
}
}
@ -936,10 +952,11 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy,
case CPUFREQ_GOV_STOP:
for_each_cpu(j, policy->cpus) {
pcpu = &per_cpu(cpuinfo, j);
down_write(&pcpu->enable_sem);
pcpu->governor_enabled = 0;
smp_wmb();
del_timer_sync(&pcpu->cpu_timer);
del_timer_sync(&pcpu->cpu_slack_timer);
up_write(&pcpu->enable_sem);
}
if (atomic_dec_return(&active_count) > 0)
@ -989,6 +1006,7 @@ static int __init cpufreq_interactive_init(void)
init_timer(&pcpu->cpu_slack_timer);
pcpu->cpu_slack_timer.function = cpufreq_interactive_nop_timer;
spin_lock_init(&pcpu->load_lock);
init_rwsem(&pcpu->enable_sem);
}
spin_lock_init(&target_loads_lock);