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

[Michel Dänzer]

On 2018-12-21 4:10 a.m., Yu Zhao wrote:
> 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.

There is no race, amdgpu_crtc->pflip_status is protected by dev->event_lock.


-- 
Earthling Michel Dänzer   |   http://www.amd.com
Libre software enthusiast | Mesa and X developer

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

[Yu Zhao]

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 
---
 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(>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(>dev->event_lock, flags);
 
 
-- 
2.20.1.415.g653613c723-goog