mutex: Always clear owner field upon mutex_unlock()

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only cleared iff debug_locks is active. This exposes a race to other users of the field where the mutex->owner may be still set to a stale value, potentially upsetting mutex_spin_on_owner() among others. References: https://bugs.freedesktop.org/show_bug.cgi?id=87955 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk Signed-off-by: Ingo Molnar <mingo@kernel.org>

mutex: Always clear owner field upon mutex_unlock()
Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only cleared iff debug_locks is active. This exposes a race to other users of the field where the mutex->owner may be still set to a stale value, potentially upsetting mutex_spin_on_owner() among others. References: https://bugs.freedesktop.org/show_bug.cgi?id=87955 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk Signed-off-by: Ingo Molnar <mingo@kernel.org>
Chris Wilson · Ingo Molnar · Eric Lee · Eric Lee · Eric Lee · Eric Lee
1 parent 11c8f01b42
Showing 1 changed file with 1 additions and 1 deletions Side-by-side Diff
kernel/locking/mutex-debug.c
@@ -80,13 +80,13 @@
 			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);
 }
...	...	@@ -80,13 +80,13 @@
80	80	DEBUG_LOCKS_WARN_ON(lock->owner != current);
81	81
82	82	DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
83		- mutex_clear_owner(lock);
84	83	}
85	84
86	85	/*
87	86	* __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
88	87	* mutexes so that we can do it here after we've verified state.
89	88	*/
	89	+ mutex_clear_owner(lock);
90	90	atomic_set(&lock->count, 1);
91	91	}
92	92