diff options
| author | Chris Wilson <chris@chris-wilson.co.uk> | 2015-01-02 09:47:10 +0000 |
|---|---|---|
| committer | Jani Nikula <jani.nikula@intel.com> | 2015-01-12 10:53:02 +0200 |
| commit | 226e5ae9e5f9108beb0bde4ac69f68fe6210fed9 (patch) | |
| tree | 3ef710700347c707757b89ea3f1e8f9c5228ddb7 | |
| parent | 48bf5b2d00bfeb681f6500c626189c7cd2c964d2 (diff) | |
drm/i915: Fix mutex->owner inspection race under DEBUG_MUTEXES
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@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
| -rw-r--r-- | drivers/gpu/drm/i915/i915_gem.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index c11603b4cf1d..76354d3ba925 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -5155,7 +5155,7 @@ 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 */ |