locking/mutex, drm: Introduce mutex_trylock_recursive()

By popular DRM demand, introduce mutex_trylock_recursive() to fix up the
two GEM users.

Without this it is very easy for these drivers to get stuck in
low-memory situations and trigger OOM. Work is in progress to remove the
need for this in at least i915.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ding Tianhong <dingtianhong@huawei.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jason Low <jason.low2@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Terry Rudd <terry.rudd@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <Will.Deacon@arm.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 12 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index e9bd2a81d03a..c450076d2f9b 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -227,11 +227,20 @@ 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))
+	switch (mutex_trylock_recursive(&dev->struct_mutex)) {
+	case MUTEX_TRYLOCK_FAILED:
 		return false;
 
-	*unlock = true;
-	return true;
+	case MUTEX_TRYLOCK_SUCCESS:
+		*unlock = true;
+		return true;
+
+	case MUTEX_TRYLOCK_RECURSIVE:
+		*unlock = false;
+		return true;
+	}
+
+	BUG();
 }
 
 static unsigned long