From: Nicolas Pitre <nicolas.pi...@linaro.org>
Relying on pcpu->governor_enabled alone to ensure proper shutdown
of the governor activities is flawed. The following race is perfectly
possible:
CPU0 |CPU2
---- +----
|cpufreq_interactive_timer()
cpufreq_governor_interactive(GOV_STOP) |if (!pcpu->governor_enabled)
pcpu->governor_enabled = 0; | return; [untaken]
smp_wmb(); |[...]
del_timer_sync(&pcpu->cpu_timer); |cpufreq_interactive_timer_resched()
|mod_timer_pinned(&pcpu->cpu_timer)
Result: timer is pending again. It is also possible for
del_timer_sync() to race against the invocation of the idle notifier
callback which also 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.
Signed-off-by: Nicolas Pitre <nicolas.pi...@linaro.org>
---
drivers/cpufreq/cpufreq_interactive.c | 38 ++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 10 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_interactive.c
b/drivers/cpufreq/cpufreq_interactive.c
index c82d9fe..061af7f 100644
--- a/drivers/cpufreq/cpufreq_interactive.c
+++ b/drivers/cpufreq/cpufreq_interactive.c
@@ -21,14 +21,13 @@
#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/tick.h>
#include <linux/time.h>
#include <linux/timer.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>
-#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm/cputime.h>
@@ -50,6 +49,7 @@ struct cpufreq_interactive_cpuinfo {
unsigned int floor_freq;
u64 floor_validate_time;
u64 hispeed_validate_time;
+ struct rw_semaphore mutex;
int governor_enabled;
};
@@ -138,8 +138,8 @@ static void cpufreq_interactive_timer(unsigned long data)
unsigned int index;
unsigned long flags;
- smp_rmb();
-
+ if (!down_read_trylock(&pcpu->mutex))
+ return;
if (!pcpu->governor_enabled)
goto exit;
@@ -258,6 +258,7 @@ rearm:
}
exit:
+ up_read(&pcpu->mutex);
return;
}
@@ -267,8 +268,12 @@ static void cpufreq_interactive_idle_start(void)
&per_cpu(cpuinfo, smp_processor_id());
int pending;
- if (!pcpu->governor_enabled)
+ if (!down_read_trylock(&pcpu->mutex))
+ return;
+ if (!pcpu->governor_enabled) {
+ up_read(&pcpu->mutex);
return;
+ }
pending = timer_pending(&pcpu->cpu_timer);
@@ -298,6 +303,7 @@ static void cpufreq_interactive_idle_start(void)
}
}
+ up_read(&pcpu->mutex);
}
static void cpufreq_interactive_idle_end(void)
@@ -305,8 +311,12 @@ 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->mutex))
+ return;
+ if (!pcpu->governor_enabled) {
+ up_read(&pcpu->mutex);
return;
+ }
/* Arm the timer for 1-2 ticks later if not already. */
if (!timer_pending(&pcpu->cpu_timer)) {
@@ -317,6 +327,8 @@ static void cpufreq_interactive_idle_end(void)
del_timer(&pcpu->cpu_timer);
cpufreq_interactive_timer(smp_processor_id());
}
+
+ up_read(&pcpu->mutex);
}
static int cpufreq_interactive_speedchange_task(void *data)
@@ -351,10 +363,12 @@ 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->mutex))
+ continue;
+ if (!pcpu->governor_enabled) {
+ up_read(&pcpu->mutex);
continue;
+ }
for_each_cpu(j, pcpu->policy->cpus) {
struct cpufreq_interactive_cpuinfo *pjcpu =
@@ -371,6 +385,8 @@ static int cpufreq_interactive_speedchange_task(void *data)
trace_cpufreq_interactive_setspeed(cpu,
pcpu->target_freq,
pcpu->policy->cur);
+
+ up_read(&pcpu->mutex);
}
}
@@ -690,9 +706,10 @@ 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->mutex);
pcpu->governor_enabled = 0;
- smp_wmb();
del_timer_sync(&pcpu->cpu_timer);
+ up_write(&pcpu->mutex);
}
if (atomic_dec_return(&active_count) > 0)
@@ -736,6 +753,7 @@ static int __init cpufreq_interactive_init(void)
init_timer_deferrable(&pcpu->cpu_timer);
pcpu->cpu_timer.function = cpufreq_interactive_timer;
pcpu->cpu_timer.data = i;
+ init_rwsem(&pcpu->mutex);
}
spin_lock_init(&speedchange_cpumask_lock);
--
1.7.12.rc2.18.g61b472e
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