Re: [PATCH] workqueue: Fix false positive stall reports

[Tejun Heo]

Hello,

On Fri, Mar 20, 2026 at 12:23:32PM -0700, Song Liu wrote:
> index b77119d71641..5b501ff1223a 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -7701,6 +7701,23 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
>  
>  		/* did we stall? */
>  		if (time_after(now, ts + thresh)) {
> +			unsigned long irq_flags;
> +
> +			raw_spin_lock_irqsave(&pool->lock, irq_flags);

Can you use guard() instead? I don't think we can just keep the lock in the
block.

> +			/*
> +			 * Recheck last_progress_ts with pool->lock, this
> +			 * eliminates false positive where we report wq
> +			 * stall for newly queued work.
> +			 */

And I think this deserves a bit more explanation. Can you move this comment
outside the block where /* did we stall? */ is and give the scenario where
it can go wrong w/o the locked check?

> +			pool_ts = READ_ONCE(pool->last_progress_ts);

pool->last_progress_ts is write protected by pool lock. No need for
READ_ONCE().

> +			if (time_after(pool_ts, touched))
> +				ts = pool_ts;
> +			else
> +				ts = touched;
> +			raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
> +			if (!time_after(now, ts + thresh))
> +				continue;

Thanks.

-- 
tejun