drm/xe: Protect against unset LRC when pausing submissions

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.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Fixes: c25c1010df88 ("drm/xe/vf: Replay GuC submission state on pause / unpause")
Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251124222853.1900800-1-tomasz.lis@intel.com
(cherry picked from commit 07cf4b864f523f01d2bb522a05813df30b076ba8)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
index c56fd44641f65533527e57da4389fcb78d22ae1b..ed7be50b2f7208ce9ce05f45cb4494a03cb6e6bf 100644 (file)
--- a/drivers/gpu/drm/xe/xe_guc_submit.c
+++ b/drivers/gpu/drm/xe/xe_guc_submit.c
@@ -2112,6 +2112,18 @@ 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
@@ -2135,8 +2147,8 @@ 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
@@ -2144,10 +2156,8 @@ 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);