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> > --- > drivers/gpu/drm/i915/i915_gem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index ad55b06a3cb1..4c14db9587a6 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -5024,7 +5024,7 @@ static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task) > if (!mutex_is_locked(mutex)) > return false; > > -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_MUTEXES) > +#if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES) > return mutex->owner == task; > #else > /* Since UP may be pre-empted, we cannot assume that we own the lock */ > -- > 2.1.4 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- 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