From badb38ce4742c752e573d2884390467ea29866c9 Mon Sep 17 00:00:00 2001 Message-Id: From: Xiaoguang Chen Date: Wed, 12 Jun 2013 17:09:49 +0800 Subject: [PATCH] cpufreq: fix governor start/stop race condition cpufreq governor stop and start should be kept in sequence. If not, there will be unexpected behavior, for example: we have 4 cpus and policy->cpu=cpu0, cpu1/2/3 are linked to cpu0. the normal sequence is as below: 1) Current governor is userspace, one application tries to set governor to ondemand. it will call __cpufreq_set_policy in which it will stop userspace governor and then start ondemand governor. 2) Current governor is userspace, now cpu0 hotplugs in cpu3, it will call cpufreq_add_policy_cpu. on which it first stops userspace governor, and then starts userspace governor. Now if the sequence of above two cases interleaves, it becames below sequence: 1) application stops userspace governor 2) hotplug stops userspace governor 3) application starts ondemand governor 4) hotplug starts a governor in step 4, hotplug is supposed to start userspace governor, but now the governor has been changed by application to ondemand, so hotplug starts ondemand governor again !!!! The solution is: do not allow stop one policy's governor multi-times Governor stop should only do once for one policy, after it is stopped, no other governor stop should be executed. also add one mutext to protect __cpufreq_governor so governor operation can be kept in sequence. Signed-off-by: Xiaoguang Chen --- drivers/cpufreq/cpufreq.c | 25 ++++++++++++++++++++++++- include/linux/cpufreq.h | 1 + 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 2d53f47..80b9798 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -46,6 +46,7 @@ static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data); static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor); #endif static DEFINE_RWLOCK(cpufreq_driver_lock); +static DEFINE_MUTEX(cpufreq_governor_lock); /* * cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure @@ -1541,7 +1542,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, #else struct cpufreq_governor *gov = NULL; #endif - if (policy->governor->max_transition_latency && policy->cpuinfo.transition_latency > policy->governor->max_transition_latency) { @@ -1562,6 +1562,21 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, pr_debug("__cpufreq_governor for CPU %u, event %u\n", policy->cpu, event); + + mutex_lock(&cpufreq_governor_lock); + if ((!policy->governor_enabled && (event == CPUFREQ_GOV_STOP)) || + (policy->governor_enabled && (event == CPUFREQ_GOV_START))) { + mutex_unlock(&cpufreq_governor_lock); + return -EBUSY; + } + + if (event == CPUFREQ_GOV_STOP) + policy->governor_enabled = 0; + else if (event == CPUFREQ_GOV_START) + policy->governor_enabled = 1; + + mutex_unlock(&cpufreq_governor_lock); + ret = policy->governor->governor(policy, event); if (!ret) { @@ -1569,6 +1584,14 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, policy->governor->initialized++; else if (event == CPUFREQ_GOV_POLICY_EXIT) policy->governor->initialized--; + } else { + /* Restore original values */ + mutex_lock(&cpufreq_governor_lock); + if (event == CPUFREQ_GOV_STOP) + policy->governor_enabled = 1; + else if (event == CPUFREQ_GOV_START) + policy->governor_enabled = 0; + mutex_unlock(&cpufreq_governor_lock); } /* we keep one module reference alive for diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 037d36a..c12db73 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -107,6 +107,7 @@ struct cpufreq_policy { unsigned int policy; /* see above */ struct cpufreq_governor *governor; /* see below */ void *governor_data; + int governor_enabled; /* governor start/stop flag */ struct work_struct update; /* if update_policy() needs to be * called, but you're in IRQ context */ -- 1.7.12.rc2.18.g61b472e