[PATCH] drm/i915/gem: Avoid NULL dereference in __i915_gem_object_lock()

[Tim Gardner]

Coverity warns of a possible NULL dereference:

Both dma_resv_lock_interruptible() and dma_resv_lock() can return -EDEADLK. 
Protect
against a NULL dereference by checking for NULL before saving the object 
pointer. This
is consistent with previous checks for ww==NULL.

Addresses-Coverity: ("Dereference after null check")

Cc: sta...@vger.kernel.org
Fixes: 80f0b679d6f0683f23cf98a511af3e44dd509472 ("drm/i915: Add an 
implementation for i915_gem_ww_ctx locking, v2.")
Cc: kernel-janit...@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
Cc: David Airlie <airl...@linux.ie>
Cc: Daniel Vetter <dan...@ffwll.ch>
Cc: intel-...@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-ker...@vger.kernel.org
Cc: linux-me...@vger.kernel.org
Cc: linaro-mm-...@lists.linaro.org
Signed-off-by: Tim Gardner <tim.gard...@canonical.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_object.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h 
b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 48112b9d76df..3391ca4f662a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -187,7 +187,7 @@ static inline int __i915_gem_object_lock(struct 
drm_i915_gem_object *obj,
        if (ret == -EALREADY)
                ret = 0;
 
-       if (ret == -EDEADLK) {
+       if (ret == -EDEADLK && ww) {
                i915_gem_object_get(obj);
                ww->contended = obj;
        }
-- 
2.33.0