Messages in this thread Patch in this message |  | | | Date | Fri, 03 Jul 2009 11:25:15 -0400 | | From | Mathieu Desnoyers <> | | Subject | [patch 2.6.30 1/4] remove rwsem lock from CPUFREQ_GOV_STOP call (second call site) |
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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 read 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 Venkyi at lock definition site.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> CC: rjw@sisk.pl CC: mingo@elte.hu CC: Shaohua Li <shaohua.li@intel.com> CC: Pekka Enberg <penberg@cs.helsinki.fi> CC: Dave Young <hidave.darkstar@gmail.com> CC: "Rafael J. Wysocki" <rjw@sisk.pl> CC: Rusty Russell <rusty@rustcorp.com.au> CC: trenn@suse.de CC: sven.wegener@stealer.net CC: cpufreq@vger.kernel.org --- drivers/cpufreq/cpufreq.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) Index: linux-2.6-lttng/drivers/cpufreq/cpufreq.c =================================================================== --- linux-2.6-lttng.orig/drivers/cpufreq/cpufreq.c 2009-06-08 12:47:22.000000000 -0400 +++ linux-2.6-lttng/drivers/cpufreq/cpufreq.c 2009-06-08 12:48:38.000000000 -0400 @@ -61,6 +61,8 @@ static DEFINE_SPINLOCK(cpufreq_driver_lo * 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 c 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; -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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