Patch "drm/amdgpu: Fix error handling in amdgpu_flip_work_func." has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

drm/amdgpu: Fix error handling in amdgpu_flip_work_func.

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-amdgpu-fix-error-handling-in-amdgpu_flip_work_func.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mario Kleiner <[email protected]>
Date: Tue, 1 Mar 2016 21:31:16 +0100
Subject: drm/amdgpu: Fix error handling in amdgpu_flip_work_func.
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From: Mario Kleiner <[email protected]>

commit 90e94b160c7f647ddffda707f5e3c0c66c170df8 upstream.

The patch e1d09dc0ccc6: "drm/amdgpu: Don't hang in amdgpu_flip_work_func on disabled crtc." from Feb 19, 2016, leads to the following static checker warning, as reported by Dan Carpenter in
https://lists.freedesktop.org/archives/dri-devel/2016-February/101987.html

drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:127 amdgpu_flip_work_func() warn: should this be 'repcnt == -1'
drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:136 amdgpu_flip_work_func() error: double unlock 'spin_lock:&crtc->dev->event_lock' drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:136 amdgpu_flip_work_func() error: double unlock 'irqsave:flags'

This patch fixes both reported problems:

Change post-decrement of repcnt to pre-decrement, so it can't underflow anymore, but still performs up to three repetitions - three is the maximum one could expect in practice.

Move the spin_unlock_irqrestore to where it actually belongs.

---
 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -96,7 +96,7 @@ static void amdgpu_flip_work_func(struct
 	 * In practice this won't execute very often unless on very fast
 	 * machines because the time window for this to happen is very small.
 	 */
-	while (amdgpuCrtc->enabled && repcnt--) {
+	while (amdgpuCrtc->enabled && --repcnt) {
 		/* GET_DISTANCE_TO_VBLANKSTART returns distance to real vblank
 		 * start in hpos, and to the "fudged earlier" vblank start in
 		 * vpos.

@@ -112,13 +112,13 @@ static void amdgpu_flip_work_func(struct
 			break;
 
 		/* Sleep at least until estimated real start of hw vblank */
-		spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
 		min_udelay = (-hpos + 1) * max(vblank->linedur_ns / 1000, 5);
 		if (min_udelay > vblank->framedur_ns / 2000) {
 			/* Don't wait ridiculously long - something is wrong */
 			repcnt = 0;
 			break;
 		}
+		spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
 		usleep_range(min_udelay, 2 * min_udelay);
 		spin_lock_irqsave(&crtc->dev->event_lock, flags);
 	};

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/drm-amdgpu-fix-error-handling-in-amdgpu_flip_work_func.patch queue-4.4/drm-radeon-fix-error-handling-in-radeon_flip_work_func.patch