drm/i915: Hold mutex across i915_gem_release

Inorder to serialise the closing of the file descriptor and its
subsequent release of client requests with i915_gem_free_request(), we
need to hold the struct_mutex in i915_gem_release(). Failing to do so
has the potential to trigger an OOPS, later with a use-after-free.

Testcase: igt/gem_close_race
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70874
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71029
Reported-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

2 files changed, 2 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 0cab2d045135..ac9dac99b585 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1848,8 +1848,10 @@ void i915_driver_lastclose(struct drm_device * dev)
 
 void i915_driver_preclose(struct drm_device * dev, struct drm_file *file_priv)
 {
+        mutex_lock(&dev->struct_mutex);
         i915_gem_context_close(dev, file_priv);
         i915_gem_release(dev, file_priv);
+        mutex_unlock(&dev->struct_mutex);
 }
 
 void i915_driver_postclose(struct drm_device *dev, struct drm_file *file)
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 72a3df32292f..4a05956162c1 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -347,10 +347,8 @@ void i915_gem_context_close(struct drm_device *dev, struct drm_file *file)
 {
         struct drm_i915_file_private *file_priv = file->driver_priv;
 
-        mutex_lock(&dev->struct_mutex);
         idr_for_each(&file_priv->context_idr, context_idr_cleanup, NULL);
         idr_destroy(&file_priv->context_idr);
-        mutex_unlock(&dev->struct_mutex);
 }
 
 static struct i915_hw_context *