On Wed, Jan 07, 2015 at 03:27:41PM +0200, Jani Nikula wrote: > On Wed, 07 Jan 2015, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > On Wed, Jan 07, 2015 at 02:12:14PM +0200, Jani Nikula wrote: > >> On Mon, 05 Jan 2015, Daniel Vetter <daniel@xxxxxxxx> wrote: > >> > On Fri, Jan 02, 2015 at 09:47:10AM +0000, Chris Wilson wrote: > >> >> If CONFIG_DEBUG_MUTEXES is set, the mutex->owner field is only cleared > >> >> if the mutex debugging is enabled which introduces a race in our > >> >> mutex_is_locked_by() - i.e. we may inspect the old owner value before it > >> >> is acquired by the new task. > >> >> > >> >> This is the root cause of this error: > >> >> > >> >> diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c > >> >> index 5cf6731..3ef3736 100644 > >> >> --- a/kernel/locking/mutex-debug.c > >> >> +++ b/kernel/locking/mutex-debug.c > >> >> @@ -80,13 +80,13 @@ void debug_mutex_unlock(struct mutex *lock) > >> >> DEBUG_LOCKS_WARN_ON(lock->owner != current); > >> >> > >> >> DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next); > >> >> - mutex_clear_owner(lock); > >> >> } > >> >> > >> >> /* > >> >> * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug > >> >> * mutexes so that we can do it here after we've verified state. > >> >> */ > >> >> + mutex_clear_owner(lock); > >> >> atomic_set(&lock->count, 1); > >> >> } > >> >> > >> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=87955 > >> >> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > >> >> Cc: stable@xxxxxxxxxxxxxxx > >> > > >> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > >> > >> Pushed to drm-intel-fixes, thanks for the patch and review. > > > > For the record, I plan to post a revert of this to -next if the core fix > > lands upstream (looks good so far). > > Does it look like that could be cc:stable? I didn't suggest it should be, so I wait with bated breath. I know disabling lock-stealing in i915 is fairly safe (some corner cases may now get oom, but that's a perenial risk anyway) and so felt more comfortable with pushing this i915 patch through stable. -Chris -- Chris Wilson, Intel Open Source Technology Centre -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html