Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756335Ab3FLJKh (ORCPT ); Wed, 12 Jun 2013 05:10:37 -0400 Received: from na3sys009aog104.obsmtp.com ([74.125.149.73]:53120 "EHLO na3sys009aog104.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754620Ab3FLJKe (ORCPT ); Wed, 12 Jun 2013 05:10:34 -0400 From: Xiaoguang Chen To: , CC: , , , , , , , Xiaoguang Chen Subject: [PATCH v4] cpufreq: fix governor start/stop race condition Date: Wed, 12 Jun 2013 17:09:49 +0800 Message-ID: <1371028189-15758-1-git-send-email-chenxg@marvell.com> X-Mailer: git-send-email 1.8.0 MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4818 Lines: 138 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 | 28 +++++++++++++++++++++++----- include/linux/cpufreq.h | 1 + 2 files changed, 24 insertions(+), 5 deletions(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 2d53f47..6c10cf0 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 @@ -896,6 +897,8 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif) goto module_out; } + + policy = kzalloc(sizeof(struct cpufreq_policy), GFP_KERNEL); if (!policy) goto nomem_out; @@ -1541,13 +1544,14 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, #else struct cpufreq_governor *gov = NULL; #endif - + mutex_lock(&cpufreq_governor_lock); if (policy->governor->max_transition_latency && policy->cpuinfo.transition_latency > policy->governor->max_transition_latency) { - if (!gov) + if (!gov) { + mutex_unlock(&cpufreq_governor_lock); return -EINVAL; - else { + } else { printk(KERN_WARNING "%s governor failed, too long" " transition latency of HW, fallback" " to %s governor\n", @@ -1557,11 +1561,19 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, } } - if (!try_module_get(policy->governor->owner)) + if (!try_module_get(policy->governor->owner)) { + mutex_unlock(&cpufreq_governor_lock); return -EINVAL; - + } pr_debug("__cpufreq_governor for CPU %u, event %u\n", policy->cpu, event); + + if ((!policy->governor_enabled && (event == CPUFREQ_GOV_STOP)) || + (policy->governor_enabled && (event == CPUFREQ_GOV_START))) { + mutex_unlock(&cpufreq_governor_lock); + return -EBUSY; + } + ret = policy->governor->governor(policy, event); if (!ret) { @@ -1569,6 +1581,10 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, policy->governor->initialized++; else if (event == CPUFREQ_GOV_POLICY_EXIT) policy->governor->initialized--; + else if (event == CPUFREQ_GOV_STOP) + policy->governor_enabled = 0; + else if (event == CPUFREQ_GOV_START) + policy->governor_enabled = 1; } /* we keep one module reference alive for @@ -1578,6 +1594,8 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, if ((event == CPUFREQ_GOV_STOP) && !ret) module_put(policy->governor->owner); + mutex_unlock(&cpufreq_governor_lock); + return ret; } 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 */ -- 1.8.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/