6.6-stable review patch. If anyone has any objections, please let me know.
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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-ekurz... 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 01da6789d0440..b3433265be6ab 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -1034,7 +1034,8 @@ 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); @@ -1103,7 +1104,8 @@ 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]); }