Re: [PATCH] drm/amd/display: Fix error handling on waiting for completion

["Michel Dänzer" <michel@daenzer.net>]

On 2021-10-26 13:07, Stylon Wang wrote:
> [Why]
> In GNOME Settings->Display the switching from mirror mode to single display
> occasionally causes wait_for_completion_interruptible_timeout() to return
> -ERESTARTSYS and fails atomic check.
> 
> [How]
> Replace the call with wait_for_completion_timeout() since the waiting for
> hw_done and flip_done completion doesn't need to worry about interruption
> from signal.
> 
> Signed-off-by: Stylon Wang <stylon.wang@amd.com>
> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 4cd64529b180..b8f4ff323de1 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -9844,10 +9844,10 @@ static int do_aquire_global_lock(struct drm_device *dev,
>  		 * Make sure all pending HW programming completed and
>  		 * page flips done
>  		 */
> -		ret = wait_for_completion_interruptible_timeout(&commit->hw_done, 10*HZ);
> +		ret = wait_for_completion_timeout(&commit->hw_done, 10*HZ);
>  
>  		if (ret > 0)
> -			ret = wait_for_completion_interruptible_timeout(
> +			ret = wait_for_completion_timeout(
>  					&commit->flip_done, 10*HZ);
>  
>  		if (ret == 0)
> 

The *_interruptible_* variant is needed so that the display manager process can be killed while it's waiting here, which could take up to 10 seconds (per the timeout).

What's the problem with -ERESTARTSYS? Either the ioctl should be restarted automatically, or if it bounces back to user space, that needs to be able to retry the ioctl while it returns -1 and errno == EINTR. drmIoctl handles this transparently.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer