diff options
| author | Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | 2009-05-17 10:23:52 -0400 |
|---|---|---|
| committer | Dave Jones <davej@redhat.com> | 2009-05-26 12:04:50 -0400 |
| commit | 42a06f2166f2f6f7bf04f32b4e823eacdceafdc9 (patch) | |
| tree | c5e08605fe4578bf1c35fab20eed520f505d767d | |
| parent | d38e73e8dad454a5916f446b0d3523c1161ae95a (diff) | |
| download | linux-42a06f2166f2f6f7bf04f32b4e823eacdceafdc9.tar.bz2 | |
[CPUFREQ] remove rwsem lock from CPUFREQ_GOV_STOP call
* Rafael J. Wysocki (rjw@sisk.pl) wrote:
> This message has been generated automatically as a part of a report
> of regressions introduced between 2.6.28 and 2.6.29.
>
> The following bug entry is on the current list of known regressions
> introduced between 2.6.28 and 2.6.29. Please verify if it still should
> be listed and let me know (either way).
>
>
> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13186
> Subject : cpufreq timer teardown problem
> Submitter : Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Date : 2009-04-23 14:00 (24 days old)
> References : http://marc.info/?l=linux-kernel&m=124049523515036&w=4
> Handled-By : Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Patch : http://patchwork.kernel.org/patch/19754/
> http://patchwork.kernel.org/patch/19753/
The patches linked above depend on the following patch to remove
circular locking dependency :
cpufreq: remove rwsem lock from CPUFREQ_GOV_STOP call
(the following issue was faced when using cancel_delayed_work_sync() in the
timer teardown (which fixes a race).
* KOSAKI Motohiro (kosaki.motohiro@jp.fujitsu.com) wrote:
> Hi
>
> my box output following warnings.
> it seems regression by commit 7ccc7608b836e58fbacf65ee4f8eefa288e86fac.
>
> A: work -> do_dbs_timer() -> cpu_policy_rwsem
> B: store() -> cpu_policy_rwsem -> cpufreq_governor_dbs() -> work
>
>
Hrm, I think it must be due to my attempt to fix the timer teardown race
in ondemand governor mixed with new locking behavior in 2.6.30-rc.
The rwlock seems to be taken around the whole call to
cpufreq_governor_dbs(), when it should be only taken around accesses to
the locked data, and especially *not* around the call to
dbs_timer_exit().
Reverting my fix attempt would put the teardown race back in place
(replacing the cancel_delayed_work_sync by cancel_delayed_work).
Instead, a proper fix would imply modifying this critical section :
cpufreq.c: __cpufreq_remove_dev()
...
if (cpufreq_driver->target)
__cpufreq_governor(data, CPUFREQ_GOV_STOP);
unlock_policy_rwsem_write(cpu);
To make sure the __cpufreq_governor() callback is not called with rwsem
held. This would allow execution of cancel_delayed_work_sync() without
being nested within the rwsem.
Applies on top of the 2.6.30-rc5 tree.
Required to remove circular dep in teardown of both conservative and
ondemande governors so they can use cancel_delayed_work_sync().
CPUFREQ_GOV_STOP does not modify the policy, therefore this locking seemed
unneeded.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Greg KH <greg@kroah.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: "Rafael J. Wysocki" <rjw@sisk.pl>
CC: Ben Slusky <sluskyb@paranoiacs.org>
CC: Chris Wright <chrisw@sous-sol.org>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>
| -rw-r--r-- | drivers/cpufreq/cpufreq.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index d270e8eb3e67..47d2ad0ae079 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1070,11 +1070,11 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev) spin_unlock_irqrestore(&cpufreq_driver_lock, flags); #endif + unlock_policy_rwsem_write(cpu); + if (cpufreq_driver->target) __cpufreq_governor(data, CPUFREQ_GOV_STOP); - unlock_policy_rwsem_write(cpu); - kobject_put(&data->kobj); /* we need to make sure that the underlying kobj is actually |