* Rafael J. Wysocki (rjw@xxxxxxx) 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@xxxxxxxxxx> > 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@xxxxxxxxxx> > 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@xxxxxxxxxxxxxx) 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@xxxxxxxxxx> CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Cc: Greg KH <greg@xxxxxxxxx> CC: Ingo Molnar <mingo@xxxxxxx> CC: "Rafael J. Wysocki" <rjw@xxxxxxx> CC: Ben Slusky <sluskyb@xxxxxxxxxxxxxx> CC: Dave Jones <davej@xxxxxxxxxx> CC: Chris Wright <chrisw@xxxxxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/cpufreq/cpufreq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: linux-2.6-lttng/drivers/cpufreq/cpufreq.c =================================================================== --- linux-2.6-lttng.orig/drivers/cpufreq/cpufreq.c 2009-05-10 14:41:53.000000000 -0400 +++ linux-2.6-lttng/drivers/cpufreq/cpufreq.c 2009-05-10 14:42:29.000000000 -0400 @@ -1070,11 +1070,11 @@ static int __cpufreq_remove_dev(struct s 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 -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
