[Intel-gfx] [PATCH] drm/i915: Serialize insertion into the file->mm.request_list

[Chris Wilson]

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 at chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 9 +++++++--
 drivers/gpu/drm/i915/i915_request.c            | 6 +++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 53752006d307..f30258eebbd2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2003,8 +2003,13 @@ 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)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 86c8dd44216b..f1a0a57fc6fc 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/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);
-- 
2.23.0.rc1