From mboxrd@z Thu Jan 1 00:00:00 1970 From: venkatesh.pallipadi-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org Subject: [patch 1/3] cpufreq: remove rwsem lock from CPUFREQ_GOV_STOP call (second call site) Date: Thu, 25 Jun 2009 11:33:55 -0700 Message-ID: <20090625183601.300706000@intel.com> References: <20090625183354.491259000@intel.com> Return-path: Content-Disposition: inline; filename=0001-remove-rwsem-lock-from-CPUFREQ_GOV_STOP-call-second.patch Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Dave Jones Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cpufreq-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Ingo Molnar , "Rafael J. Wysocki" , Dave Young , Pekka Enberg , Mathieu Desnoyers , Thomas Renninger , Venkatesh Pallipadi From: Mathieu Desnoyers commit 42a06f2166f2f6f7bf04f32b4e823eacdceafdc9 Missed a call site for CPUFREQ_GOV_STOP to remove the rwlock taken around the teardown. To make a long story short, the rwlock write-lock causes a circular dependency with cancel_delayed_work_sync(), because the timer handler takes the write lock. Note that all callers to __cpufreq_set_policy are taking the rwsem. All sysfs callers (writers) hold the write rwsem at the earliest sysfs calling stage. However, the rwlock write-lock is not needed upon governor stop. Change : - Added comment from Venki at lock definition site. Signed-off-by: Mathieu Desnoyers Signed-off-by: Thomas Renninger Signed-off-by: Venkatesh Pallipadi --- drivers/cpufreq/cpufreq.c | 13 ++++++++++++- 1 files changed, 12 insertions(+), 1 deletions(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 6e2ec0b..728656c 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -61,6 +61,8 @@ static DEFINE_SPINLOCK(cpufreq_driver_lock); * are concerned with are online after they get the lock. * - Governor routines that can be called in cpufreq hotplug path should not * take this sem as top level hotplug notifier handler takes this. + * - Lock should not be held across + * __cpufreq_governor(data, CPUFREQ_GOV_STOP); */ static DEFINE_PER_CPU(int, policy_cpu); static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem); @@ -1697,8 +1699,17 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data, dprintk("governor switch\n"); /* end old governor */ - if (data->governor) + if (data->governor) { + /* + * Need to release the rwsem around governor + * stop due to lock dependency between + * cancel_delayed_work_sync and the read lock + * taken in the delayed work handler. + */ + unlock_policy_rwsem_write(data->cpu); __cpufreq_governor(data, CPUFREQ_GOV_STOP); + lock_policy_rwsem_write(data->cpu); + } /* start new governor */ data->governor = policy->governor; -- 1.6.0.6 --