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

["Kazlauskas, Nicholas" <nicholas.kazlauskas@amd.com>]

On 2021-10-26 7:07 a.m., 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>

I think this is okay, but I'll write out how I think these work here in 
case anyone has corrections.

Both variants allow the thread to sleep, but the interruptible variant 
can waken due to signals. These signals are a secondary wakeup event and 
would require use to restart the wait and (probably) keep track of how 
long we were waiting before.

We want wakeup only on completion, so we should be using the 
`wait_for_completion_timeout()` variants instead in most (if not all?) 
cases in our display driver.

This probably has some nuances that matter more for different variants 
of UAPI, but with this understanding I think this is:

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>

Now, if we could revive that patch series I had from the other year and 
outright drop `do_aquire_global_lock()`...

Regards,
Nicholas Kazlauskas

> ---
>   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)
>