[PATCH 1/3] drm/amd: fix race in page flip job

From: Yu Zhao
Date: Thu Dec 20 2018 - 22:11:28 EST

Fix race between page flip job submission and completion. We invoke
page_flip callback to submit page flip job to GPU first and then set
pflip_status. If GPU fires page flip done irq in between, its handler
won't see the correct pflip_status thus will refuse to notify the job
completion. The job will eventually times out.

Reverse the order of calling page_flip and setting pflip_status to
fix the race.

Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
index 686a26de50f9..e309d26170db 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
@@ -105,11 +105,11 @@ static void amdgpu_display_flip_work_func(struct work_struct *__work)
/* We borrow the event spin lock for protecting flip_status */
spin_lock_irqsave(&crtc->dev->event_lock, flags);

+ /* Set the flip status */
+ amdgpu_crtc->pflip_status = AMDGPU_FLIP_SUBMITTED;
/* Do the flip (mmio) */
adev->mode_info.funcs->page_flip(adev, work->crtc_id, work->base, work->async);

- /* Set the flip status */
- amdgpu_crtc->pflip_status = AMDGPU_FLIP_SUBMITTED;
spin_unlock_irqrestore(&crtc->dev->event_lock, flags);