releases/4.4.6/drm-amdgpu-fix-error-handling-in-amdgpu_flip_work_func.patch

From 90e94b160c7f647ddffda707f5e3c0c66c170df8 Mon Sep 17 00:00:00 2001
From: Mario Kleiner <mario.kleiner.de@gmail.com>
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 <mario.kleiner.de@gmail.com>

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.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
@@ -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);
 	};