[PATCH] drm/amd/display: Add NULL checks for vblank workqueue

[Harry Wentland]

On 2021-09-07 10:10 a.m., Nicholas Kazlauskas wrote:
> [Why]
> If we're running a headless config with 0 links then the vblank
> workqueue will be NULL - causing a NULL pointer exception during
> any commit.
> 
> [How]
> Guard access to the workqueue if it's NULL and don't queue or flush
> work if it is.
> 
> Cc: Roman Li <Roman.Li at amd.com>
> Cc: Wayne Lin <Wayne.Lin at amd.com>
> Cc: Harry Wentland <Harry.Wentland at amd.com>
> Reported-by: Mike Lothian <mike at fireburn.co.uk>
> BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1700
> Fixes: 91f86d4cce2 ("drm/amd/display: Use vblank control events for PSR enable/disable")
> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 32 +++++++++++--------
>  1 file changed, 18 insertions(+), 14 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 8837259215d..46e08736f94 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -6185,21 +6185,23 @@ static inline int dm_set_vblank(struct drm_crtc *crtc, bool enable)
>  		return 0;
>  
>  #if defined(CONFIG_DRM_AMD_DC_DCN)
> -	work = kzalloc(sizeof(*work), GFP_ATOMIC);
> -	if (!work)
> -		return -ENOMEM;
> +	if (dm->vblank_control_workqueue) {
> +		work = kzalloc(sizeof(*work), GFP_ATOMIC);
> +		if (!work)
> +			return -ENOMEM;
>  
> -	INIT_WORK(&work->work, vblank_control_worker);
> -	work->dm = dm;
> -	work->acrtc = acrtc;
> -	work->enable = enable;
> +		INIT_WORK(&work->work, vblank_control_worker);
> +		work->dm = dm;
> +		work->acrtc = acrtc;
> +		work->enable = enable;
>  
> -	if (acrtc_state->stream) {
> -		dc_stream_retain(acrtc_state->stream);
> -		work->stream = acrtc_state->stream;
> -	}
> +		if (acrtc_state->stream) {
> +			dc_stream_retain(acrtc_state->stream);
> +			work->stream = acrtc_state->stream;
> +		}
>  
> -	queue_work(dm->vblank_control_workqueue, &work->work);
> +		queue_work(dm->vblank_control_workqueue, &work->work);
> +	}
>  #endif
>  
>  	return 0;
> @@ -8809,7 +8811,8 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
>  		 * If PSR or idle optimizations are enabled then flush out
>  		 * any pending work before hardware programming.
>  		 */
> -		flush_workqueue(dm->vblank_control_workqueue);
> +		if (dm->vblank_control_workqueue)
> +			flush_workqueue(dm->vblank_control_workqueue);
>  #endif
>  
>  		bundle->stream_update.stream = acrtc_state->stream;
> @@ -9144,7 +9147,8 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
>  		/* if there mode set or reset, disable eDP PSR */
>  		if (mode_set_reset_required) {
>  #if defined(CONFIG_DRM_AMD_DC_DCN)
> -			flush_workqueue(dm->vblank_control_workqueue);
> +			if (dm->vblank_control_workqueue)
> +				flush_workqueue(dm->vblank_control_workqueue);
>  #endif
>  			amdgpu_dm_psr_disable_all(dm);
>  		}
>