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

[Nirmoy Das]

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 at intel.com>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3233
Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
---
 drivers/gpu/drm/xe/xe_sync.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_sync.c b/drivers/gpu/drm/xe/xe_sync.c
index a90480c6aecf..42f5bebd09e5 100644
--- a/drivers/gpu/drm/xe/xe_sync.c
+++ b/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);
 }
 
-- 
2.46.0