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/067537.html v1 -> v2: adjust lockdep_assert_none_held_once condition Fixes: 01d6c3578379 ("drm/syncobj: add support for timeline point wait v8") Signed-off-by: Erik Kurzinger <ekurzinger@xxxxxxxxxx> --- drivers/gpu/drm/drm_syncobj.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 94ebc71e5be5..97be8b140599 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -1058,7 +1058,8 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs, uint64_t *points; uint32_t signaled_count, i; - if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) + if (flags & (DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT | + DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE)) lockdep_assert_none_held_once(); points = kmalloc_array(count, sizeof(*points), GFP_KERNEL); @@ -1127,7 +1128,8 @@ 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
