[PATCH 5.4 82/84] drm/syncobj: call drm_syncobj_fence_add_wait when WAIT_AVAILABLE flag is set

Greg Kroah-Hartman
2024-02-27T14:25:17Z

From: Erik Kurzinger <ekurzinger@nvidia.com>

[ Upstream commit 3c43177ffb54ea5be97505eb8e2690e99ac96bc9 ]

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

(cherry picked from commit 8c44ea81634a4a337df70a32621a5f3791be23df)

Fixes: 01d6c3578379 ("drm/syncobj: add support for timeline point wait v8")
Signed-off-by: Erik Kurzinger <ekurzinger@nvidia.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20240119163208.3723457-1-ekurzinger@nvidia.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 a1d2a3dc00768..9baf95a4fc9ff 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -898,7 +898,8 @@ 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);
@@ -967,7 +968,8 @@ 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