This is a note to let you know that I've just added the patch titled
drm/i915: Fix mutex->owner inspection race under DEBUG_MUTEXES
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-i915-fix-mutex-owner-inspection-race-under-debug_mutexes.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 226e5ae9e5f9108beb0bde4ac69f68fe6210fed9 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Date: Fri, 2 Jan 2015 09:47:10 +0000
Subject: drm/i915: Fix mutex->owner inspection race under DEBUG_MUTEXES
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 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 mu
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 */
Patches currently in stable-queue which might be from chris@xxxxxxxxxxxxxxxxxx are
queue-3.10/drm-i915-fix-mutex-owner-inspection-race-under-debug_mutexes.patch
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