drm/xe/ufence: Wake up waiters after setting ufence->signalled

If a previous ufence is not signalled, vm_bind will return -EBUSY.
Delaying the modification of ufence->signalled can cause issues if the
UMD reuses the same ufence so update ufence->signalled before waking up
waiters.

Cc: Matthew Brost <matthew.brost@intel.com>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3233
Fixes: 977e5b8 ("drm/xe: Expose user fence from xe_sync_entry")
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241114150537.4161573-1-nirmoy.das@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
(cherry picked from commit 553a5d1)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: nirmoy

drivers/gpu/drm/xe/xe_sync.c

@@ -87,8 +87,12 @@ static void user_fence_worker(struct work_struct *w)
 		drm_dbg(&ufence->xe->drm, "mmget_not_zero() failed, ufence wasn't signaled\n");
 	}
 
-	wake_up_all(&ufence->xe->ufence_wq);
+	/*
+	 * Wake up waiters only after updating the ufence state, allowing the UMD
+	 * to safely reuse the same ufence without encountering -EBUSY errors.
+	 */
 	WRITE_ONCE(ufence->signalled, 1);
+	wake_up_all(&ufence->xe->ufence_wq);
 	user_fence_put(ufence);
 }