Re: [PATCH v1 05/14] cxl/mem: Add 20 second timeout for stalled DC event chains

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] cxl/mem: handle_dcd_chain_event() queues work on deprecated system_wq
--

commit ffea09425b5b7122c1c8acbc05e99f66a63015a7
Author: Anisa Su <anisa.su887@gmail.com>

cxl/mem: Add 20 second timeout for stalled DC event chains

This commit adds a 20-second delayed-work watchdog to abort Dynamic Capacity
event chains when a device opens a chain with CXL_DCD_EVENT_MORE set but
never sends the closing record. On timeout, an add capacity chain is refused
with an empty response while a release capacity chain is cleared for retry.

> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 3acf5ace48dbc..fea910e6c5108 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c

[ ... ]

> @@ -1279,9 +1343,22 @@ static int handle_dcd_chain_event(struct cxl_memdev_state *mds,
>  
>  	if (event->flags & CXL_DCD_EVENT_MORE) {
>  		dev_dbg(dev, "more bit set; delay processing of extent\n");
> +		/* The deadline is fixed when the chain opens, not per record */
> +		if (!chain->armed) {
> +			queue_delayed_work(system_wq, &chain->timeout_work,
> +					   CXL_DC_CHAIN_TIMEOUT);
> +			chain->armed = true;
> +		}

[Severity: Low]
When a Dynamic Capacity event record arrives with CXL_DCD_EVENT_MORE set,
handle_dcd_chain_event() queues chain->timeout_work onto system_wq.

In include/linux/workqueue.h, system_wq is marked deprecated in favor of
system_percpu_wq:

extern struct workqueue_struct *system_wq; /* use system_percpu_wq, this will be removed */
extern struct workqueue_struct *system_percpu_wq;

Because system_wq is allocated with __WQ_DEPRECATED, when the 20-second timer
expires and delayed_work_timer_fn() dispatches the work via __queue_work(),
it triggers a runtime deprecation warning:

	if (unlikely(wq->flags & __WQ_DEPRECATED))
		pr_warn_once("workqueue: work func %ps enqueued on deprecated workqueue. "
			"Use system_{percpu|dfl}_wq instead.\n",
			work->func);

Should handle_dcd_chain_event() use schedule_delayed_work() or
system_percpu_wq instead of system_wq?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261104230445.66625-1-anisa.su@samsung.com?part=5