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Date: Thu, 18 Feb 2016 18:58:58 +0100 From: "Rafael J. Wysocki" <rjw@...ysocki.net> To: Viresh Kumar <viresh.kumar@...aro.org> Cc: Linux PM list <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: [PATCH v2 12/12] cpufreq: governor: Narrow down the dbs_data_mutex coverage On Thursday, February 18, 2016 11:50:40 AM Viresh Kumar wrote: > On 18-02-16, 02:38, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com> [cut] > > This has turned into an ugly maze, really. I think it would be much > better if we sacrifice a bit on consistency in the code, and move the > locks in cpufreq_governor_dbs() around invocations to > cpufreq_governor_init(). Or maybe create a > __cpufreq_governor_init(), or whatever. > > That routine is hardly readably anymore. So does the one below look better? --- From: Rafael J. Wysocki <rafael.j.wysocki@...el.com> Subject: [PATCH] cpufreq: governor: Narrow down the dbs_data_mutex coverage Since cpufreq_governor_dbs() is now always called with policy->rwsem held, it cannot be executed twice in parallel for the same policy. Thus it is not necessary to hold dbs_data_mutex around the invocations of cpufreq_governor_start/stop/limits() from it as those functions never modify any data that can be shared between different policies. However, cpufreq_governor_dbs() may be executed twice in parallal for different policies using the same gov->gdbs_data object and dbs_data_mutex is still necessary to protect that object against concurrent updates. For this reason, narrow down the dbs_data_mutex locking to cpufreq_governor_init/exit() where it is needed and rename the mutex to gov_dbs_data_mutex to reflect its purpose. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com> --- drivers/cpufreq/cpufreq_governor.c | 46 ++++++++++++++++++------------------- 1 file changed, 23 insertions(+), 23 deletions(-) Index: linux-pm/drivers/cpufreq/cpufreq_governor.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c +++ linux-pm/drivers/cpufreq/cpufreq_governor.c @@ -24,7 +24,7 @@ static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs); -static DEFINE_MUTEX(dbs_data_mutex); +static DEFINE_MUTEX(gov_dbs_data_mutex); /* Common sysfs tunables */ /** @@ -422,10 +422,10 @@ static void free_policy_dbs_info(struct static int cpufreq_governor_init(struct cpufreq_policy *policy) { struct dbs_governor *gov = dbs_governor_of(policy); - struct dbs_data *dbs_data = gov->gdbs_data; + struct dbs_data *dbs_data; struct policy_dbs_info *policy_dbs; unsigned int latency; - int ret; + int ret = 0; /* State should be equivalent to EXIT */ if (policy->governor_data) @@ -435,6 +435,10 @@ static int cpufreq_governor_init(struct if (!policy_dbs) return -ENOMEM; + /* Protect gov->gdbs_data against concurrent updates. */ + mutex_lock(&gov_dbs_data_mutex); + + dbs_data = gov->gdbs_data; if (dbs_data) { if (WARN_ON(have_governor_per_policy())) { ret = -EINVAL; @@ -447,8 +451,7 @@ static int cpufreq_governor_init(struct dbs_data->usage_count++; list_add(&policy_dbs->list, &dbs_data->policy_dbs_list); mutex_unlock(&dbs_data->mutex); - - return 0; + goto out; } dbs_data = kzalloc(sizeof(*dbs_data), GFP_KERNEL); @@ -489,7 +492,7 @@ static int cpufreq_governor_init(struct get_governor_parent_kobj(policy), "%s", gov->gov.name); if (!ret) - return 0; + goto out; /* Failure, so roll back. */ pr_err("cpufreq: Governor initialization failed (dbs_data kobject init error %d)\n", ret); @@ -503,6 +506,9 @@ static int cpufreq_governor_init(struct free_policy_dbs_info: free_policy_dbs_info(policy, gov); + +out: + mutex_unlock(&gov_dbs_data_mutex); return ret; } @@ -513,6 +519,9 @@ static int cpufreq_governor_exit(struct struct dbs_data *dbs_data = policy_dbs->dbs_data; int count; + /* Protect gov->gdbs_data against concurrent updates. */ + mutex_lock(&gov_dbs_data_mutex); + mutex_lock(&dbs_data->mutex); list_del(&policy_dbs->list); count = --dbs_data->usage_count; @@ -534,6 +543,8 @@ static int cpufreq_governor_exit(struct } free_policy_dbs_info(policy, gov); + + mutex_unlock(&gov_dbs_data_mutex); return 0; } @@ -600,31 +611,20 @@ static int cpufreq_governor_limits(struc int cpufreq_governor_dbs(struct cpufreq_policy *policy, unsigned int event) { - int ret = -EINVAL; - - /* Lock governor to block concurrent initialization of governor */ - mutex_lock(&dbs_data_mutex); - if (event == CPUFREQ_GOV_POLICY_INIT) { - ret = cpufreq_governor_init(policy); + return cpufreq_governor_init(policy); } else if (policy->governor_data) { switch (event) { case CPUFREQ_GOV_POLICY_EXIT: - ret = cpufreq_governor_exit(policy); - break; + return cpufreq_governor_exit(policy); case CPUFREQ_GOV_START: - ret = cpufreq_governor_start(policy); - break; + return cpufreq_governor_start(policy); case CPUFREQ_GOV_STOP: - ret = cpufreq_governor_stop(policy); - break; + return cpufreq_governor_stop(policy); case CPUFREQ_GOV_LIMITS: - ret = cpufreq_governor_limits(policy); - break; + return cpufreq_governor_limits(policy); } } - - mutex_unlock(&dbs_data_mutex); - return ret; + return -EINVAL; } EXPORT_SYMBOL_GPL(cpufreq_governor_dbs);
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