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

[Breno Leitao]

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@xxxxxxxxxx>

Acked-by: Breno Leitao <leitao@xxxxxxxxxx>