[PATCH] drm/syncobj: call drm_syncobj_fence_add_wait when, WAIT_AVAILABLE flag is set

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When waiting for a syncobj timeline point whose fence has not yet been
submitted with the WAIT_FOR_SUBMIT flag, a callback is registered using
drm_syncobj_fence_add_wait and the thread is put to sleep until the
timeout expires. If the fence is submitted before then,
drm_syncobj_add_point will wake up the sleeping thread immediately which
will proceed to wait for the fence to be signaled.

However, if the WAIT_AVAILABLE flag is used instead,
drm_syncobj_fence_add_wait won't get called, meaning the waiting thread
will always sleep for the full timeout duration, even if the fence gets
submitted earlier. If it turns out that the fence *has* been submitted
by the time it eventually wakes up, it will still indicate to userspace
that the wait completed successfully (it won't return -ETIME), but it
will have taken much longer than it should have.

To fix this, we must call drm_syncobj_fence_add_wait if *either* the
WAIT_FOR_SUBMIT flag or the WAIT_AVAILABLE flag is set. The only
difference being that with WAIT_FOR_SUBMIT we will also wait for the
fence to be signaled after it has been submitted while with
WAIT_AVAILABLE we will return immediately.

IGT test patch: https://lists.freedesktop.org/archives/igt-dev/2024-January/067282.html

Fixes: 01d6c3578379 ("drm/syncobj: add support for timeline point wait v8")
Signed-off-by: Erik Kurzinger <ekurzinger@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_syncobj.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index a8e6b61a188c..a1443c673f30 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1121,7 +1121,8 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
 	 * fallthough and try a 0 timeout wait!
 	 */
 
-	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) {
+	if (flags & (DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT |
+		     DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE)) {
 		for (i = 0; i < count; ++i)
 			drm_syncobj_fence_add_wait(syncobjs[i], &entries[i]);
 	}
-- 
2.43.0





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