[PATCH] drm/sched: test before reading fence timestamp

[Christian König]

Am 08.09.23 um 20:24 schrieb Yunxiang Li:
> Reading fence timestamp always need to check the corresponding flag bit
> before to make sure the write is actually visible, otherwise we can read
> garbage here.

Yeah, Teddy already stumbled over that problem as well I think.

We are currently testing a more wider fix for this.

Regards,
Christian.

>
> Fixes: 1774baa64f93 ("drm/scheduler: Change scheduled fence track v2")
> Signed-off-by: Yunxiang Li <Yunxiang.Li at amd.com>
> ---
>   drivers/gpu/drm/scheduler/sched_main.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 506371c42745..8ed00f54c59d 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -928,6 +928,9 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
>   						typeof(*next), list);
>   
>   		if (next) {
> +			while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
> +					 &job->s_fence->finished.flags))
> +				cpu_relax();
>   			next->s_fence->scheduled.timestamp =
>   				job->s_fence->finished.timestamp;
>   			/* start TO timer for next job */