From: Todd Poynor Date: Wed, 19 Dec 2012 01:50:44 +0000 (-0800) Subject: cpufreq: interactive: fix racy timer stopping X-Git-Tag: firefly_0821_release~4090^2~615 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=beb55c19d504f6d8fd7cd1c019027d67d4b4084a;p=firefly-linux-kernel-4.4.55.git 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 --- diff --git a/drivers/cpufreq/cpufreq_interactive.c b/drivers/cpufreq/cpufreq_interactive.c index f8e9ee9f7137..74f56093d2f3 100644 --- a/drivers/cpufreq/cpufreq_interactive.c +++ b/drivers/cpufreq/cpufreq_interactive.c @@ -21,7 +21,7 @@ #include #include #include -#include +#include #include #include #include @@ -29,7 +29,6 @@ #include #include #include -#include #include #include @@ -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);