Messages in this thread | | | Date | Thu, 29 Sep 2022 16:57:55 +0200 | Subject | Re: [PATCH v4 5/6] drm/sched: Use parent fence instead of finished | From | Christian König <> |
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Am 29.09.22 um 16:53 schrieb Steven Price: > On 14/09/2022 17:43, Arvind Yadav wrote: >> Using the parent fence instead of the finished fence >> to get the job status. This change is to avoid GPU >> scheduler timeout error which can cause GPU reset. > I'm able to reproduce crashes on Panfrost and I believe this commit is > the cause. Specifically it's possible for job->s_fence->parent to be NULL. > > The underlying issue seems to involve drm_sched_resubmit_jobs_ext() - if > the run_jobs() callback returns an error it will set s_fence->parent to > NULL after signalling s_fence->finished: > >> fence = sched->ops->run_job(s_job); >> i++; >> >> if (IS_ERR_OR_NULL(fence)) { >> if (IS_ERR(fence)) >> dma_fence_set_error(&s_fence->finished, PTR_ERR(fence)); >> >> s_job->s_fence->parent = NULL; > I don't understand the reasoning behind this change, but it doesn't seem > right to be using the parent fence when we have code which can be > setting that pointer to NULL. > > Since I don't understand the reasoning my only suggestion is to revert > this patch (and potentially the dependent patch "dma-buf: Check status > of enable-signaling bit on debug"?). > > Can anyone suggest a better fix?
Well, first of all please absolutely don't use drm_sched_resubmit_jobs_ext()!
It was an extremely bad idea in amdgpu to approach GPU by re-submitting jobs and it was an even worse idea to push this into the scheduler.
The design of dma_fence is that you submit that once and *only* once and then get a result for this submission. If re-submission is desirable it should be done in userspace or at least higher levels.
Apart from that, yes a NULL check is missing here but that should be trivial to fix.
Thanks, Christian.
> > Thanks, > > Steve > >> Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com> >> Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >> --- >> >> changes in v1,v2 - Enable signaling for finished fence in sche_main() >> is removed >> >> --- >> drivers/gpu/drm/scheduler/sched_main.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c >> index e0ab14e0fb6b..2ac28ad11432 100644 >> --- a/drivers/gpu/drm/scheduler/sched_main.c >> +++ b/drivers/gpu/drm/scheduler/sched_main.c >> @@ -829,7 +829,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched) >> job = list_first_entry_or_null(&sched->pending_list, >> struct drm_sched_job, list); >> >> - if (job && dma_fence_is_signaled(&job->s_fence->finished)) { >> + if (job && dma_fence_is_signaled(job->s_fence->parent)) { >> /* remove job from pending_list */ >> list_del_init(&job->list); >> >> @@ -841,7 +841,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched) >> >> if (next) { >> next->s_fence->scheduled.timestamp = >> - job->s_fence->finished.timestamp; >> + job->s_fence->parent->timestamp; >> /* start TO timer for next job */ >> drm_sched_start_timeout(sched); >> }
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