Re: [PATCH] workqueue: Do not warn when cancelling WQ_MEM_RECLAIM work from !WQ_MEM_RECLAIM worker

[Tejun Heo <tj@kernel.org>]

On Thu, Dec 19, 2024 at 09:30:30AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
> 
> After commit
> 746ae46c1113 ("drm/sched: Mark scheduler work queues with WQ_MEM_RECLAIM")
> amdgpu started seeing the following warning:
> 
>  [ ] workqueue: WQ_MEM_RECLAIM sdma0:drm_sched_run_job_work [gpu_sched] is flushing !WQ_MEM_RECLAIM events:amdgpu_device_delay_enable_gfx_off [amdgpu]
> ...
>  [ ] Workqueue: sdma0 drm_sched_run_job_work [gpu_sched]
> ...
>  [ ] Call Trace:
>  [ ]  <TASK>
> ...
>  [ ]  ? check_flush_dependency+0xf5/0x110
> ...
>  [ ]  cancel_delayed_work_sync+0x6e/0x80
>  [ ]  amdgpu_gfx_off_ctrl+0xab/0x140 [amdgpu]
>  [ ]  amdgpu_ring_alloc+0x40/0x50 [amdgpu]
>  [ ]  amdgpu_ib_schedule+0xf4/0x810 [amdgpu]
>  [ ]  ? drm_sched_run_job_work+0x22c/0x430 [gpu_sched]
>  [ ]  amdgpu_job_run+0xaa/0x1f0 [amdgpu]
>  [ ]  drm_sched_run_job_work+0x257/0x430 [gpu_sched]
>  [ ]  process_one_work+0x217/0x720
> ...
>  [ ]  </TASK>
> 
> The intent of the verifcation done in check_flush_depedency is to ensure
> forward progress during memory reclaim, by flagging cases when either a
> memory reclaim process, or a memory reclaim work item is flushed from a
> context not marked as memory reclaim safe.
> 
> This is correct when flushing, but when called from the
> cancel(_delayed)_work_sync() paths it is a false positive because work is
> either already running, or will not be running at all. Therefore
> cancelling it is safe and we can relax the warning criteria by letting the
> helper know of the calling context.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
> Fixes: fca839c00a12 ("workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue")
> References: 746ae46c1113 ("drm/sched: Mark scheduler work queues with WQ_MEM_RECLAIM")
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: <stable@vger.kernel.org> # v4.5+

Applied to wq/for-6.13-fixes.

Thanks.

-- 
tejun