[tip:locking/core] locking/drm: Fix i915_gem_shrinker_lock() locking

From: tip-bot for Ingo Molnar
Date: Thu Nov 03 2016 - 02:27:46 EST

Commit-ID: c7faee2109f978f3ef826c48b7e60609061fda4f
Gitweb: http://git.kernel.org/tip/c7faee2109f978f3ef826c48b7e60609061fda4f
Author: Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Thu, 3 Nov 2016 07:16:43 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 3 Nov 2016 07:21:12 +0100

locking/drm: Fix i915_gem_shrinker_lock() locking

Mike Krinkin reported hangs in the DRM code and bisected it to:

3ab7c086d5ec72585ef0 ("locking/drm: Kill mutex trickery")

Hugh Dickins observed:

"i915_gem_shrinker_lock() is broken: but copy the pattern from
msm_gem_shrinker_lock() and it's okay - patch below."

Pick up the fix in isolation to make sure the bug is fixed, cleanup
patch will follow up.

Originally-From: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: Mike Krinkin <krinkin.m.u@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: chris@xxxxxxxxxxxxxxxxxx
Cc: jason.low2@xxxxxxx
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1610301645180.28429@xxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
drivers/gpu/drm/i915/i915_gem_shrinker.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index 3695375..e9bd2a8 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -228,8 +228,9 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv)
static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
if (!mutex_trylock(&dev->struct_mutex))
- *unlock = false;
+ return false;

+ *unlock = true;
return true;