From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 226e5ae9e5f9108beb0bde4ac69f68fe6210fed9 upstream. 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> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- 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 ef5fe7e9d86c..7e4e6896fa81 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -4795,7 +4795,7 @@ 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 */ -- 2.2.2 -- 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