[PATCH v2 1/3] drm/syncobj: call drm_syncobj_fence_add_wait when WAIT_AVAILABLE flag is set

[Daniel Vetter]

On Fri, Jan 19, 2024 at 08:32:06AM -0800, Erik Kurzinger wrote:
> 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 at nvidia.com>

Yeah I think this series catches now all the corner cases I spotted in v1.
On the series:

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch