From: Venki Pallipadi Date: Fri, 26 Oct 2007 17:18:21 +0000 (-0700) Subject: [CPUFREQ] Eliminate cpufreq_userspace scaling_setspeed deadlock X-Git-Tag: v2.6.25-rc1~302^2~6 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9e76988e9390a4ff4d171f690586d0c58186b47e;p=linux-2.6 [CPUFREQ] Eliminate cpufreq_userspace scaling_setspeed deadlock Eliminate cpufreq_userspace scaling_setspeed deadlock. Luming Yu recently uncovered yet another cpufreq related deadlock. One thread that continuously switches the governors and the other thread that repeatedly cats the contents of cpufreq directory causes both these threads to go into a deadlock. Detailed examination of the deadlock showed the exact flow before the deadlock as: Thread 1 Thread 2 ________ ________ cats files under /sys/devices/.../cpufreq/ Set governor to userspace Adds a new sysfs entry for scaling_setspeed cats files under /sys/devices/.../cpufreq/ Set governor to performance Holds cpufreq_rw_sem in write mode Sends a STOP notify to userspace governor cat /sys/devices/.../cpufreq/scaling_setspeed Gets a handle on the above sysfs entry with sysfs_get_active Blocks while trying to get cpufreq_rw_sem in read mode Remove a sysfs entry for scaling_setspeed Blocks on sysfs_deactivate while waiting for earlier get_active (on other thread) to drain At this point both threads go into deadlock and any other thread that tries to do anything with sysfs cpufreq will also block. There seems to be no easy way to avoid this deadlock as long as cpufreq_userspace adds/removes the sysfs entry under same kobject as cpufreq. Below patch moves scaling_setspeed to cpufreq.c, keeping it always and calling back the governor on read/write. This is the cleanest fix I could think of, even though adding two callbacks in governor structure just for this seems unnecessary. Note that the change makes scaling_setspeed under /sys/.../cpufreq permanent and returns when governor is not userspace. Signed-off-by: Venkatesh Pallipadi Signed-off-by: Dave Jones --- diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 613314851e..64926aa990 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -601,6 +601,31 @@ static ssize_t show_affected_cpus (struct cpufreq_policy * policy, char *buf) return i; } +static ssize_t store_scaling_setspeed(struct cpufreq_policy *policy, + const char *buf, size_t count) +{ + unsigned int freq = 0; + unsigned int ret; + + if (!policy->governor->store_setspeed) + return -EINVAL; + + ret = sscanf(buf, "%u", &freq); + if (ret != 1) + return -EINVAL; + + policy->governor->store_setspeed(policy, freq); + + return count; +} + +static ssize_t show_scaling_setspeed(struct cpufreq_policy *policy, char *buf) +{ + if (!policy->governor->show_setspeed) + return sprintf(buf, "\n"); + + return policy->governor->show_setspeed(policy, buf); +} #define define_one_ro(_name) \ static struct freq_attr _name = \ @@ -624,6 +649,7 @@ define_one_ro(affected_cpus); define_one_rw(scaling_min_freq); define_one_rw(scaling_max_freq); define_one_rw(scaling_governor); +define_one_rw(scaling_setspeed); static struct attribute * default_attrs[] = { &cpuinfo_min_freq.attr, @@ -634,6 +660,7 @@ static struct attribute * default_attrs[] = { &scaling_governor.attr, &scaling_driver.attr, &scaling_available_governors.attr, + &scaling_setspeed.attr, NULL }; diff --git a/drivers/cpufreq/cpufreq_userspace.c b/drivers/cpufreq/cpufreq_userspace.c index f8cdde4bf6..cb2ac01a41 100644 --- a/drivers/cpufreq/cpufreq_userspace.c +++ b/drivers/cpufreq/cpufreq_userspace.c @@ -65,12 +65,12 @@ static struct notifier_block userspace_cpufreq_notifier_block = { /** * cpufreq_set - set the CPU frequency + * @policy: pointer to policy struct where freq is being set * @freq: target frequency in kHz - * @cpu: CPU for which the frequency is to be set * * Sets the CPU frequency to freq. */ -static int cpufreq_set(unsigned int freq, struct cpufreq_policy *policy) +static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq) { int ret = -EINVAL; @@ -102,34 +102,11 @@ static int cpufreq_set(unsigned int freq, struct cpufreq_policy *policy) } -/************************** sysfs interface ************************/ -static ssize_t show_speed (struct cpufreq_policy *policy, char *buf) +static ssize_t show_speed(struct cpufreq_policy *policy, char *buf) { - return sprintf (buf, "%u\n", cpu_cur_freq[policy->cpu]); + return sprintf(buf, "%u\n", cpu_cur_freq[policy->cpu]); } -static ssize_t -store_speed (struct cpufreq_policy *policy, const char *buf, size_t count) -{ - unsigned int freq = 0; - unsigned int ret; - - ret = sscanf (buf, "%u", &freq); - if (ret != 1) - return -EINVAL; - - cpufreq_set(freq, policy); - - return count; -} - -static struct freq_attr freq_attr_scaling_setspeed = -{ - .attr = { .name = "scaling_setspeed", .mode = 0644 }, - .show = show_speed, - .store = store_speed, -}; - static int cpufreq_governor_userspace(struct cpufreq_policy *policy, unsigned int event) { @@ -142,10 +119,6 @@ static int cpufreq_governor_userspace(struct cpufreq_policy *policy, return -EINVAL; BUG_ON(!policy->cur); mutex_lock(&userspace_mutex); - rc = sysfs_create_file (&policy->kobj, - &freq_attr_scaling_setspeed.attr); - if (rc) - goto start_out; if (cpus_using_userspace_governor == 0) { cpufreq_register_notifier( @@ -160,7 +133,7 @@ static int cpufreq_governor_userspace(struct cpufreq_policy *policy, cpu_cur_freq[cpu] = policy->cur; cpu_set_freq[cpu] = policy->cur; dprintk("managing cpu %u started (%u - %u kHz, currently %u kHz)\n", cpu, cpu_min_freq[cpu], cpu_max_freq[cpu], cpu_cur_freq[cpu]); -start_out: + mutex_unlock(&userspace_mutex); break; case CPUFREQ_GOV_STOP: @@ -176,7 +149,6 @@ start_out: cpu_min_freq[cpu] = 0; cpu_max_freq[cpu] = 0; cpu_set_freq[cpu] = 0; - sysfs_remove_file (&policy->kobj, &freq_attr_scaling_setspeed.attr); dprintk("managing cpu %u stopped\n", cpu); mutex_unlock(&userspace_mutex); break; @@ -211,6 +183,8 @@ start_out: struct cpufreq_governor cpufreq_gov_userspace = { .name = "userspace", .governor = cpufreq_governor_userspace, + .store_setspeed = cpufreq_set, + .show_setspeed = show_speed, .owner = THIS_MODULE, }; EXPORT_SYMBOL(cpufreq_gov_userspace); diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 23932d7741..ddd8652fc3 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -167,6 +167,10 @@ struct cpufreq_governor { char name[CPUFREQ_NAME_LEN]; int (*governor) (struct cpufreq_policy *policy, unsigned int event); + ssize_t (*show_setspeed) (struct cpufreq_policy *policy, + char *buf); + int (*store_setspeed) (struct cpufreq_policy *policy, + unsigned int freq); unsigned int max_transition_latency; /* HW must be able to switch to next freq faster than this value in nano secs or we will fallback to performance governor */