drm/i915: Simplify releasing context reference

A few users only take the struct_mutex in order to release a reference
to a context. We can expose a kref_put_mutex() wrapper in order to
simplify these users, and optimise taking of the mutex to the final
unref.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161218153724.8439-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -3518,6 +3518,13 @@ static inline void i915_gem_context_put(struct i915_gem_context *ctx)
 	kref_put(&ctx->ref, i915_gem_context_free);
 }
 
+static inline void i915_gem_context_put_unlocked(struct i915_gem_context *ctx)
+{
+	kref_put_mutex(&ctx->ref,
+		       i915_gem_context_free,
+		       &ctx->i915->drm.struct_mutex);
+}
+
 static inline struct intel_timeline *
 i915_gem_context_lookup_timeline(struct i915_gem_context *ctx,
 				 struct intel_engine_cs *engine)

drivers/gpu/drm/i915/i915_perf.c

@@ -1555,8 +1555,6 @@ static long i915_perf_ioctl(struct file *file,
  */
 static void i915_perf_destroy_locked(struct i915_perf_stream *stream)
 {
-	struct drm_i915_private *dev_priv = stream->dev_priv;
-
 	if (stream->enabled)
 		i915_perf_disable_locked(stream);
 
@@ -1565,11 +1563,8 @@ static void i915_perf_destroy_locked(struct i915_perf_stream *stream)
 
 	list_del(&stream->link);
 
-	if (stream->ctx) {
-		mutex_lock(&dev_priv->drm.struct_mutex);
-		i915_gem_context_put(stream->ctx);
-		mutex_unlock(&dev_priv->drm.struct_mutex);
-	}
+	if (stream->ctx)
+		i915_gem_context_put_unlocked(stream->ctx);
 
 	kfree(stream);
 }
@@ -1738,11 +1733,8 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
 err_alloc:
 	kfree(stream);
 err_ctx:
-	if (specific_ctx) {
-		mutex_lock(&dev_priv->drm.struct_mutex);
-		i915_gem_context_put(specific_ctx);
-		mutex_unlock(&dev_priv->drm.struct_mutex);
-	}
+	if (specific_ctx)
+		i915_gem_context_put_unlocked(specific_ctx);
 err:
 	return ret;
 }