drm/i915: Serialize insertion into the file->mm.request_list

Currently, we remove the from per-file request list for throttling and
retirement under a dedicated spinlock, but insertion is governed by
struct_mutex. This needs to be the same lock so that the
retirement/insertion of neighbouring requests (at the tail) doesn't
break the list.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190820080907.4665-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -2005,8 +2005,13 @@ static struct i915_vma *eb_parse(struct i915_execbuffer *eb, bool is_master)
 static void
 add_to_client(struct i915_request *rq, struct drm_file *file)
 {
-	rq->file_priv = file->driver_priv;
-	list_add_tail(&rq->client_link, &rq->file_priv->mm.request_list);
+	struct drm_i915_file_private *file_priv = file->driver_priv;
+
+	rq->file_priv = file_priv;
+
+	spin_lock(&file_priv->mm.lock);
+	list_add_tail(&rq->client_link, &file_priv->mm.request_list);
+	spin_unlock(&file_priv->mm.lock);
 }
 
 static int eb_submit(struct i915_execbuffer *eb)

drivers/gpu/drm/i915/i915_request.c

@@ -165,11 +165,11 @@ static void __notify_execute_cb(struct i915_request *rq)
 }
 
 static inline void
-i915_request_remove_from_client(struct i915_request *request)
+remove_from_client(struct i915_request *request)
 {
 	struct drm_i915_file_private *file_priv;
 
-	file_priv = request->file_priv;
+	file_priv = READ_ONCE(request->file_priv);
 	if (!file_priv)
 		return;
 
@@ -282,7 +282,7 @@ static bool i915_request_retire(struct i915_request *rq)
 
 	local_irq_enable();
 
-	i915_request_remove_from_client(rq);
+	remove_from_client(rq);
 	list_del(&rq->link);
 
 	intel_context_exit(rq->hw_context);