Re: [PATCH v1] drm/xe: Protect against unset LRC when pausing submissions

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Nov 24, 2025 at 10:23:25PM +0100, Tomasz Lis wrote:
> While pausing submissions, it is possible to encouner an exec queue
> which is during creation, and therefore doesn't have a valid xe_lrc
> struct reference.
> 
> Protect agains such situation, by checking for NULL before access.
> 

Fixes tag?

> Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>

Otherwise LGTM:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_guc_submit.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
> index 7e0882074a99..f57000c2cb9d 100644
> --- a/drivers/gpu/drm/xe/xe_guc_submit.c
> +++ b/drivers/gpu/drm/xe/xe_guc_submit.c
> @@ -2107,6 +2107,18 @@ static void guc_exec_queue_revert_pending_state_change(struct xe_guc *guc,
>  	q->guc->resume_time = 0;
>  }
>  
> +static void lrc_parallel_clear(struct xe_lrc *lrc)
> +{
> +	struct xe_device *xe = gt_to_xe(lrc->gt);
> +	struct iosys_map map = xe_lrc_parallel_map(lrc);
> +	int i;
> +
> +	for (i = 0; i < WQ_SIZE / sizeof(u32); ++i)
> +		parallel_write(xe, map, wq[i],
> +			       FIELD_PREP(WQ_TYPE_MASK, WQ_TYPE_NOOP) |
> +			       FIELD_PREP(WQ_LEN_MASK, 0));
> +}
> +
>  /*
>   * This function is quite complex but only real way to ensure no state is lost
>   * during VF resume flows. The function scans the queue state, make adjustments
> @@ -2130,8 +2142,8 @@ static void guc_exec_queue_pause(struct xe_guc *guc, struct xe_exec_queue *q)
>  	guc_exec_queue_revert_pending_state_change(guc, q);
>  
>  	if (xe_exec_queue_is_parallel(q)) {
> -		struct xe_device *xe = guc_to_xe(guc);
> -		struct iosys_map map = xe_lrc_parallel_map(q->lrc[0]);
> +		/* Pairs with WRITE_ONCE in __xe_exec_queue_init  */
> +		struct xe_lrc *lrc = READ_ONCE(q->lrc[0]);
>  
>  		/*
>  		 * NOP existing WQ commands that may contain stale GGTT
> @@ -2139,10 +2151,8 @@ static void guc_exec_queue_pause(struct xe_guc *guc, struct xe_exec_queue *q)
>  		 * seems to get confused if the WQ head/tail pointers are
>  		 * adjusted.
>  		 */
> -		for (i = 0; i < WQ_SIZE / sizeof(u32); ++i)
> -			parallel_write(xe, map, wq[i],
> -				       FIELD_PREP(WQ_TYPE_MASK, WQ_TYPE_NOOP) |
> -				       FIELD_PREP(WQ_LEN_MASK, 0));
> +		if (lrc)
> +			lrc_parallel_clear(lrc);
>  	}
>  
>  	job = xe_sched_first_pending_job(sched);
> -- 
> 2.25.1
>