From: Breno Leitao <leitao@debian.org>
To: Song Liu <song@kernel.org>
Cc: linux-kernel@vger.kernel.org, tj@kernel.org,
jiangshanlai@gmail.com, pmladek@suse.com, kernel-team@meta.com,
puranjay@kernel.org
Subject: Re: [PATCH] workqueue: Fix false positive stall reports
Date: Mon, 23 Mar 2026 02:35:20 -0700 [thread overview]
Message-ID: <acEJSviR8LSb6xRO@gmail.com> (raw)
In-Reply-To: <20260320192332.1726079-1-song@kernel.org>
On Fri, Mar 20, 2026 at 12:23:32PM -0700, Song Liu wrote:
> On weakly ordered architectures (e.g., arm64), the lockless check in
> wq_watchdog_timer_fn() can observe a reordering between the worklist
> insertion and the last_progress_ts update. Specifically, the watchdog
> can see a non-empty worklist (from a list_add) while reading a stale
> last_progress_ts value, causing a false positive stall report.
>
> This was confirmed by reading pool->last_progress_ts again after holding
> pool->lock in wq_watchdog_timer_fn():
>
> workqueue watchdog: pool 7 false positive detected!
> lockless_ts=4784580465 locked_ts=4785033728
> diff=453263ms worklist_empty=0
>
> To avoid slowing down the hot path (queue_work, etc.), recheck
> last_progress_ts with pool->lock held. This will eliminate the false
> positive with minimal overhead.
>
> Remove two extra empty lines in wq_watchdog_timer_fn() as we are on it.
>
> Assisted-by: claude-code:claude-opus-4-6
> Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Breno Leitao <leitao@debian.org>
prev parent reply other threads:[~2026-03-23 9:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-20 19:23 [PATCH] workqueue: Fix false positive stall reports Song Liu
2026-03-21 18:27 ` Tejun Heo
2026-03-23 9:35 ` Breno Leitao [this message]
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