diff options
| author | Chris Wilson <chris@chris-wilson.co.uk> | 2015-01-02 09:47:10 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-01-29 17:40:55 -0800 |
| commit | b78dc65fd7e4fb2cd2ca6ef6866eb2989fb8ee6c (patch) | |
| tree | 5cca015403e22e0192d8cb7800d4b4dd74ff77f6 | |
| parent | 0d9928f365c2bbbab82a3f56c0c612343cd260d1 (diff) | |
drm/i915: Fix mutex->owner inspection race under DEBUG_MUTEXES
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@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 0a30088178b0..0b71a0aaf4fc 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -4449,7 +4449,7 @@ 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 */ |