[PATCH 3.18 12/24] Revert "Revert "drm/i915: Fix mutex->owner inspection race under DEBUG_MUTEXES""

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

This reverts commit bc07ee33284ac6e6872d5efad1b321ec0b7b46a4. Which is
upstream commit a50940510e94f5fb65ffd79877a60592d85598a9.

This revert relies on upstream commit a63b03e2d24 ("mutex: Always clear
owner field upon mutex_unlock()") being in the tree, but that commit
should not be backported.

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 d0f0a7943d88..d88dbedeaa77 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5144,7 +5144,7 @@ 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 */
-- 
2.17.1