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cpufreq: interactive: fix racy timer stopping
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>
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1 changed files with 28 additions and 10 deletions
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@ -21,7 +21,7 @@
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#include <linux/cpufreq.h>
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/mutex.h>
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#include <linux/rwsem.h>
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#include <linux/sched.h>
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#include <linux/sched/rt.h>
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#include <linux/tick.h>
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@ -29,7 +29,6 @@
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#include <linux/timer.h>
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#include <linux/workqueue.h>
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#include <linux/kthread.h>
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#include <linux/mutex.h>
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#include <linux/slab.h>
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#include <asm/cputime.h>
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@ -52,6 +51,7 @@ struct cpufreq_interactive_cpuinfo {
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unsigned int floor_freq;
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u64 floor_validate_time;
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u64 hispeed_validate_time;
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struct rw_semaphore enable_sem;
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int governor_enabled;
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};
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@ -279,8 +279,8 @@ static void cpufreq_interactive_timer(unsigned long data)
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unsigned long flags;
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bool boosted;
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smp_rmb();
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if (!down_read_trylock(&pcpu->enable_sem))
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return;
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if (!pcpu->governor_enabled)
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goto exit;
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@ -387,6 +387,7 @@ rearm:
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cpufreq_interactive_timer_resched(pcpu);
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exit:
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up_read(&pcpu->enable_sem);
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return;
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}
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@ -396,8 +397,12 @@ static void cpufreq_interactive_idle_start(void)
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&per_cpu(cpuinfo, smp_processor_id());
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int pending;
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if (!pcpu->governor_enabled)
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if (!down_read_trylock(&pcpu->enable_sem))
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return;
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if (!pcpu->governor_enabled) {
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up_read(&pcpu->enable_sem);
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return;
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}
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pending = timer_pending(&pcpu->cpu_timer);
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@ -414,6 +419,7 @@ static void cpufreq_interactive_idle_start(void)
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cpufreq_interactive_timer_resched(pcpu);
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}
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up_read(&pcpu->enable_sem);
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}
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static void cpufreq_interactive_idle_end(void)
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@ -421,8 +427,12 @@ static void cpufreq_interactive_idle_end(void)
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struct cpufreq_interactive_cpuinfo *pcpu =
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&per_cpu(cpuinfo, smp_processor_id());
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if (!pcpu->governor_enabled)
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if (!down_read_trylock(&pcpu->enable_sem))
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return;
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if (!pcpu->governor_enabled) {
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up_read(&pcpu->enable_sem);
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return;
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}
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/* Arm the timer for 1-2 ticks later if not already. */
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if (!timer_pending(&pcpu->cpu_timer)) {
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@ -432,6 +442,8 @@ static void cpufreq_interactive_idle_end(void)
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del_timer(&pcpu->cpu_slack_timer);
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cpufreq_interactive_timer(smp_processor_id());
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}
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up_read(&pcpu->enable_sem);
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}
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static int cpufreq_interactive_speedchange_task(void *data)
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@ -466,10 +478,12 @@ static int cpufreq_interactive_speedchange_task(void *data)
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unsigned int max_freq = 0;
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pcpu = &per_cpu(cpuinfo, cpu);
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smp_rmb();
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if (!pcpu->governor_enabled)
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if (!down_read_trylock(&pcpu->enable_sem))
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continue;
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if (!pcpu->governor_enabled) {
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up_read(&pcpu->enable_sem);
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continue;
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}
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for_each_cpu(j, pcpu->policy->cpus) {
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struct cpufreq_interactive_cpuinfo *pjcpu =
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@ -486,6 +500,8 @@ static int cpufreq_interactive_speedchange_task(void *data)
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trace_cpufreq_interactive_setspeed(cpu,
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pcpu->target_freq,
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pcpu->policy->cur);
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up_read(&pcpu->enable_sem);
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}
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}
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@ -936,10 +952,11 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy,
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case CPUFREQ_GOV_STOP:
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for_each_cpu(j, policy->cpus) {
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pcpu = &per_cpu(cpuinfo, j);
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down_write(&pcpu->enable_sem);
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pcpu->governor_enabled = 0;
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smp_wmb();
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del_timer_sync(&pcpu->cpu_timer);
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del_timer_sync(&pcpu->cpu_slack_timer);
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up_write(&pcpu->enable_sem);
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}
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if (atomic_dec_return(&active_count) > 0)
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@ -989,6 +1006,7 @@ static int __init cpufreq_interactive_init(void)
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init_timer(&pcpu->cpu_slack_timer);
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pcpu->cpu_slack_timer.function = cpufreq_interactive_nop_timer;
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spin_lock_init(&pcpu->load_lock);
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init_rwsem(&pcpu->enable_sem);
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}
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spin_lock_init(&target_loads_lock);
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