On Mon, 2009-06-08 at 08:23 -0700, Mathieu Desnoyers wrote: > * Dave Jones (davej@xxxxxxxxxx) wrote: > > On Mon, Jun 08, 2009 at 08:48:45AM -0400, Mathieu Desnoyers wrote: > > > > > > > >> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13475 > > > > > >> Subject : suspend/hibernate lockdep warning > > > > > >> References : http://marc.info/?l=linux-kernel&m=124393723321241&w=4 > > > > > > > > > > I suspect the following commit, after revert this patch I test 5 times > > > > > without lockdep warnings. > > > > > > > > > > commit b14893a62c73af0eca414cfed505b8c09efc613c > > > > > Author: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> > > > > > Date: Sun May 17 10:30:45 2009 -0400 > > > > > > > > > > [CPUFREQ] fix timer teardown in ondemand governor > > > > > > > > The patch is probably not at fault here. I suspect it's some latent bug > > > > that simply got exposed by the change to cancel_delayed_work_sync(). In > > > > any case, Mathieu, can you take a look at this please? > > > > > > Yes, it's been looked at and discussed on the cpufreq ML. The short > > > answer is that they plan to re-engineer cpufreq and remove the policy > > > rwlock taken around almost every operations at the cpufreq level. > > > > > > The short-term solution, which is recognised as ugly, would be do to the > > > following before doing the cancel_delayed_work_sync() : > > > > > > unlock policy rwlock write lock > > > > > > lock policy rwlock write lock > > > > > > It basically works because this rwlock is unneeded for teardown, hence > > > the future re-work planned. > > > > > > I'm sorry I cannot prepare a patch current... I've got quite a few pages > > > of Ph.D. thesis due for the beginning of July. > > > > I'm kinda scared to touch this code at all for .30 due to the number of > > unexpected gotchas we seem to run into every time we touch something > > locking related. So I'm inclined to just live with the lockdep warning > > for .30, and see how the real fixes look for .31, and push them back > > as -stable updates if they work out. > > > > > > Venki, what are your thoughts? > > > > Hi Dave, > > I've looked through the cpufreq code, and the following patch should > address the call site I've missed in commit > 42a06f2166f2f6f7bf04f32b4e823eacdceafdc9. I've followed all > __cpufreq_set_policy call sites within cpufreq.c to make sure they all > hold the rwsem write lock. An extra round of review would be good > though. > > Can someone try the following patch and see if it fixes the regression ? > My test machine is currently busy running long formal verifications, and > therefore unavailable for kernel patch testing. It compiles fine on a > 2.6.30-rc5 kernel with my (now mainlined) cpufreq patches applied. > > Mathieu > > > remove rwsem lock from CPUFREQ_GOV_STOP call (second call site) > > 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. > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx> This change is same as the patch that I was testing right now. Only additional change I had was a comment for cpu_policy_rwsem * 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); */ Thanks, Venki > CC: rjw@xxxxxxx > CC: mingo@xxxxxxx > CC: Shaohua Li <shaohua.li@xxxxxxxxx> > CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > CC: Dave Young <hidave.darkstar@xxxxxxxxx> > CC: "Rafael J. Wysocki" <rjw@xxxxxxx> > CC: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > CC: trenn@xxxxxxx > CC: sven.wegener@xxxxxxxxxxx > CC: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx> > CC: cpufreq@xxxxxxxxxxxxxxx > --- > drivers/cpufreq/cpufreq.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > Index: linux-2.6-lttng/drivers/cpufreq/cpufreq.c > =================================================================== > --- linux-2.6-lttng.orig/drivers/cpufreq/cpufreq.c 2009-06-08 10:20:48.000000000 -0400 > +++ linux-2.6-lttng/drivers/cpufreq/cpufreq.c 2009-06-08 10:48:52.000000000 -0400 > @@ -1697,8 +1697,17 @@ 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; > > -- 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
