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

   1 From 90e94b160c7f647ddffda707f5e3c0c66c170df8 Mon Sep 17 00:00:00 2001
   2 From: Mario Kleiner <mario.kleiner.de@gmail.com>
   3 Date: Tue, 1 Mar 2016 21:31:16 +0100
   4 Subject: drm/amdgpu: Fix error handling in amdgpu_flip_work_func.
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   8
   9 From: Mario Kleiner <mario.kleiner.de@gmail.com>
  10
  11 commit 90e94b160c7f647ddffda707f5e3c0c66c170df8 upstream.
  12
  13 The patch e1d09dc0ccc6: "drm/amdgpu: Don't hang in
  14 amdgpu_flip_work_func on disabled crtc." from Feb 19, 2016, leads to
  15 the following static checker warning, as reported by Dan Carpenter in
  16 https://lists.freedesktop.org/archives/dri-devel/2016-February/101987.html
  17
  18 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:127 amdgpu_flip_work_func() warn: should this be 'repcnt == -1'
  19 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:136 amdgpu_flip_work_func() error: double unlock 'spin_lock:&crtc->dev->event_lock'
  20 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c:136 amdgpu_flip_work_func() error: double unlock 'irqsave:flags'
  21
  22 This patch fixes both reported problems:
  23
  24 Change post-decrement of repcnt to pre-decrement, so
  25 it can't underflow anymore, but still performs up to
  26 three repetitions - three is the maximum one could
  27 expect in practice.
  28
  29 Move the spin_unlock_irqrestore to where it actually
  30 belongs.
  31
  32 Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
  33 Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
  34 Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
  35 Cc: Michel Dänzer <michel.daenzer@amd.com>
  36 Cc: Alex Deucher <alexander.deucher@amd.com>
  37 Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
  38 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  39
  40 ---
  41  drivers/gpu/drm/amd/amdgpu/amdgpu_display.c |    4 ++--
  42  1 file changed, 2 insertions(+), 2 deletions(-)
  43
  44 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
  45 +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
  46 @@ -96,7 +96,7 @@ static void amdgpu_flip_work_func(struct
  47          * In practice this won't execute very often unless on very fast
  48          * machines because the time window for this to happen is very small.
  49          */
  50 -       while (amdgpuCrtc->enabled && repcnt--) {
  51 +       while (amdgpuCrtc->enabled && --repcnt) {
  52                 /* GET_DISTANCE_TO_VBLANKSTART returns distance to real vblank
  53                  * start in hpos, and to the "fudged earlier" vblank start in
  54                  * vpos.
  55 @@ -112,13 +112,13 @@ static void amdgpu_flip_work_func(struct
  56                         break;
  57
  58                 /* Sleep at least until estimated real start of hw vblank */
  59 -               spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
  60                 min_udelay = (-hpos + 1) * max(vblank->linedur_ns / 1000, 5);
  61                 if (min_udelay > vblank->framedur_ns / 2000) {
  62                         /* Don't wait ridiculously long - something is wrong */
  63                         repcnt = 0;
  64                         break;
  65                 }
  66 +               spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
  67                 usleep_range(min_udelay, 2 * min_udelay);
  68                 spin_lock_irqsave(&crtc->dev->event_lock, flags);
  69         };