From 1a6efaf68e207302cd9423051b8091fa663bbabe Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 21 Jul 2015 13:46:45 +0100
Subject: [PATCH] drm: Detect no-op drmModeAtomicRequest and return early
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If the number of items to process in the request is zero, we can forgo
duplicating, sorting the request and feeding it into the kernel and
instead report success immediately.  This prevents a NULL dereference of
the sorted->items for the no-op request.

Fixes: ed44e0b9585c563905447eceed12af9c1c7ca8d4
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rob Clark <robclark@freedesktop.org>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
---
 xf86drmMode.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xf86drmMode.c b/xf86drmMode.c
index 529429e8..fa219861 100644
--- a/xf86drmMode.c
+++ b/xf86drmMode.c
@@ -1289,7 +1289,7 @@ static int sort_req_list(const void *misc, const void *other)
 int drmModeAtomicCommit(int fd, drmModeAtomicReqPtr req, uint32_t flags,
 			void *user_data)
 {
-	drmModeAtomicReqPtr sorted = drmModeAtomicDuplicate(req);
+	drmModeAtomicReqPtr sorted;
 	struct drm_mode_atomic atomic;
 	uint32_t *objs_ptr = NULL;
 	uint32_t *count_props_ptr = NULL;
@@ -1300,7 +1300,11 @@ int drmModeAtomicCommit(int fd, drmModeAtomicReqPtr req, uint32_t flags,
 	int obj_idx = -1;
 	int ret = -1;
 
-	if (!sorted)
+	if (req->cursor == 0)
+		return 0;
+
+	sorted = drmModeAtomicDuplicate(req);
+	if (sorted == NULL)
 		return -ENOMEM;
 
 	memclear(atomic);