On 29/09/2022 15:57, Christian König wrote:
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()!
Panfrost isn't using drm_sched_resubmit_jobs_ext() directly but via drm_sched_resubmit_jobs().
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.
Panfrost has an interesting feature where it's possible to rescue a job during a GPU reset. Because jobs are queued on the GPU if the job hasn't actually started executing then it's quite possible to safely resubmit it from the kernel driver and user space doesn't need to be involved.
The benefit of this is if another process has hung the GPU that processes jobs can be killed off without affecting any other innocent processes.
One option would be to hide all this from the scheduler, but I can't see how to do that without also hiding the actual reset from the scheduler. Admittedly at the moment Panfrost is far too aggressive at resetting and will perform a GPU reset in conditions where it's completely unnecessary. There's work to do there but I haven't had the time to look at it yet.
Apart from that, yes a NULL check is missing here but that should be trivial to fix.
What I'm struggling to get my head round is whether it's correct to always treat the job as signalled just because s_fence->parent is NULL?
Thanks,
Steve
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); }