[PATCH v3] drm/xe/sched: stop re-submitting signalled jobs

[Upadhyay, Tejas]

> -----Original Message-----
> From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of
> Matthew Auld
> Sent: 28 May 2025 17:03
> To: intel-xe at lists.freedesktop.org
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>; Brost, Matthew
> <matthew.brost at intel.com>; Tseng, William <william.tseng at intel.com>;
> stable at vger.kernel.org
> Subject: [PATCH v3] drm/xe/sched: stop re-submitting signalled jobs
> 
> Customer is reporting a really subtle issue where we get random DMAR faults,
> hangs and other nasties for kernel migration jobs when stressing stuff like
> s2idle/s3/s4. The explosions seems to happen somewhere after resuming the
> system with splats looking something like:
> 
> PM: suspend exit
> rfkill: input handler disabled
> xe 0000:00:02.0: [drm] GT0: Engine reset: engine_class=bcs, logical_mask:
> 0x2, guc_id=0 xe 0000:00:02.0: [drm] GT0: Timedout job: seqno=24496,
> lrc_seqno=24496, guc_id=0, flags=0x13 in no process [-1] xe 0000:00:02.0:
> [drm] GT0: Kernel-submitted job timed out
> 
> The likely cause appears to be a race between suspend cancelling the worker
> that processes the free_job()'s, such that we still have pending jobs to be
> freed after the cancel. Following from this, on resume the pending_list will
> now contain at least one already complete job, but it looks like we call
> drm_sched_resubmit_jobs(), which will then call
> run_job() on everything still on the pending_list. But if the job was already
> complete, then all the resources tied to the job, like the bb itself, any memory
> that is being accessed, the iommu mappings etc. might be long gone since
> those are usually tied to the fence signalling.
> 
> This scenario can be seen in ftrace when running a slightly modified xe_pm
> (kernel was only modified to inject artificial latency into free_job to make the
> race easier to hit):
> 
> xe_sched_job_run: dev=0000:00:02.0, fence=0xffff888276cc8540, seqno=0,
> lrc_seqno=0, gt=0, guc_id=0, batch_addr=0x000000146910 ...
> xe_exec_queue_stop:   dev=0000:00:02.0, 3:0x2, gt=0, width=1, guc_id=0,
> guc_state=0x0, flags=0x13
> xe_exec_queue_stop:   dev=0000:00:02.0, 3:0x2, gt=0, width=1, guc_id=1,
> guc_state=0x0, flags=0x4
> xe_exec_queue_stop:   dev=0000:00:02.0, 4:0x1, gt=1, width=1, guc_id=0,
> guc_state=0x0, flags=0x3
> xe_exec_queue_stop:   dev=0000:00:02.0, 1:0x1, gt=1, width=1, guc_id=1,
> guc_state=0x0, flags=0x3
> xe_exec_queue_stop:   dev=0000:00:02.0, 4:0x1, gt=1, width=1, guc_id=2,
> guc_state=0x0, flags=0x3
> xe_exec_queue_resubmit: dev=0000:00:02.0, 3:0x2, gt=0, width=1, guc_id=0,
> guc_state=0x0, flags=0x13
> xe_sched_job_run: dev=0000:00:02.0, fence=0xffff888276cc8540, seqno=0,
> lrc_seqno=0, gt=0, guc_id=0, batch_addr=0x000000146910 ...
> .....
> xe_exec_queue_memory_cat_error: dev=0000:00:02.0, 3:0x2, gt=0, width=1,
> guc_id=0, guc_state=0x3, flags=0x13
> 
> So the job_run() is clearly triggered twice for the same job, even though the
> first must have already signalled to completion during suspend. We can also
> see a CAT error after the re-submit.
> 
> To prevent this try to call xe_sched_stop() to forcefully remove anything on
> the pending_list that has already signalled, before we re-submit.
> 
> v2:
>   - Make sure to re-arm the fence callbacks with sched_start().
> v3 (Matt B):
>   - Stop using drm_sched_resubmit_jobs(), which appears to be deprecated
>     and just open-code a simple loop such that we skip calling run_job()
>     and anything already signalled.
> 
> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4856
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> Cc: William Tseng <william.tseng at intel.com>
> Cc: <stable at vger.kernel.org> # v6.8+
> ---
>  drivers/gpu/drm/xe/xe_gpu_scheduler.h | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gpu_scheduler.h
> b/drivers/gpu/drm/xe/xe_gpu_scheduler.h
> index c250ea773491..308061f0cf37 100644
> --- a/drivers/gpu/drm/xe/xe_gpu_scheduler.h
> +++ b/drivers/gpu/drm/xe/xe_gpu_scheduler.h
> @@ -51,7 +51,15 @@ static inline void xe_sched_tdr_queue_imm(struct
> xe_gpu_scheduler *sched)
> 
>  static inline void xe_sched_resubmit_jobs(struct xe_gpu_scheduler *sched)  {
> -	drm_sched_resubmit_jobs(&sched->base);
> +	struct drm_sched_job *s_job;
> +
> +	list_for_each_entry(s_job, &sched->base.pending_list, list) {
> +		struct drm_sched_fence *s_fence = s_job->s_fence;
> +		struct dma_fence *hw_fence = s_fence->parent;
> +
> +		if (hw_fence && !dma_fence_is_signaled(hw_fence))
> +			sched->base.ops->run_job(s_job);
> +	}

While this change looks correct, what about those hanging contexts which is indicated to waiters by dma_fence_set_error(&s_fence->finished, -ECANCELED);!

Tejas
>  }
> 
>  static inline bool
> --
> 2.49.0