drm/xe: Enforce correct user fence signaling order using

Prevent application hangs caused by out-of-order fence signaling when
user fences are attached. Use drm_syncobj (via dma-fence-chain) to
guarantee that each user fence signals in order, regardless of the
signaling order of the attached fences. Ensure user fence writebacks to
user space occur in the correct sequence.

v7:
 - Skip drm_syncbj create of error (CI)

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20251031234050.3043507-2-matthew.brost@intel.com

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
index 1b57d7c2cc94..e3414b337569 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue.c
+++ b/drivers/gpu/drm/xe/xe_exec_queue.c
@@ -10,6 +10,7 @@
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
+#include <drm/drm_syncobj.h>
 #include <uapi/drm/xe_drm.h>
 
 #include "xe_dep_scheduler.h"
@@ -368,6 +369,16 @@ struct xe_exec_queue *xe_exec_queue_create_bind(struct xe_device *xe,
 	}
 	xe_vm_put(migrate_vm);
 
+	if (!IS_ERR(q)) {
+		int err = drm_syncobj_create(&q->ufence_syncobj,
+					     DRM_SYNCOBJ_CREATE_SIGNALED,
+					     NULL);
+		if (err) {
+			xe_exec_queue_put(q);
+			return ERR_PTR(err);
+		}
+	}
+
 	return q;
 }
 ALLOW_ERROR_INJECTION(xe_exec_queue_create_bind, ERRNO);
@@ -379,6 +390,9 @@ void xe_exec_queue_destroy(struct kref *ref)
 
 	xe_assert(gt_to_xe(q->gt), atomic_read(&q->job_cnt) == 0);
 
+	if (q->ufence_syncobj)
+		drm_syncobj_put(q->ufence_syncobj);
+
 	if (xe_exec_queue_uses_pxp(q))
 		xe_pxp_exec_queue_remove(gt_to_xe(q->gt)->pxp, q);