linux-kernel - Re: [PATCH v2] workqueue: Remove the warning in wq_worker

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Date:   Fri, 3 Apr 2020 10:53:26 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     kernel test robot <lkp@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, LKP <lkp@...ts.01.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2] workqueue: Remove the warning in wq_worker_sleeping()

Hello,

On Sat, Mar 28, 2020 at 12:29:59AM +0100, Sebastian Andrzej Siewior wrote:
> The kernel test robot triggered a warning with the following race:
>    task-ctx A                            interrupt-ctx B
>  worker
>   -> process_one_work()
>     -> work_item()
>       -> schedule();
>          -> sched_submit_work()
>            -> wq_worker_sleeping()
>              -> ->sleeping = 1
>                atomic_dec_and_test(nr_running)
>          __schedule();                *interrupt*
>                                        async_page_fault()
>                                        -> local_irq_enable();
>                                        -> schedule();
>                                           -> sched_submit_work()
>                                             -> wq_worker_sleeping()
>                                                -> if (WARN_ON(->sleeping)) return
>                                           -> __schedule()
>                                             ->  sched_update_worker()
>                                               -> wq_worker_running()
>                                                  -> atomic_inc(nr_running);
>                                                  -> ->sleeping = 0;
> 
>       ->  sched_update_worker()
>         -> wq_worker_running()
>           if (!->sleeping) return
> 
> In this context the warning is pointless everything is fine.

This is not a usual control flow, right? Can we annotate this case specifically
instead of weakening santiy check for generic cases?

Thanks.

-- 
tejun