linux-kernel - Re: [PATCH 1/2] workqueue: pin the pool while it is managing

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Message-ID: <CAJhGHyDVkyouuNpSDiJ9nwxZAwKd7uGWf4PN6GXE2Y+3zENz0Q@mail.gmail.com>
Date:   Fri, 29 May 2020 13:33:11 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH 1/2] workqueue: pin the pool while it is managing

On Thu, May 28, 2020 at 10:35 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Thu, May 28, 2020 at 03:06:55AM +0000, Lai Jiangshan wrote:
> > @@ -2129,10 +2128,21 @@ __acquires(&pool->lock)
> >  static bool manage_workers(struct worker *worker)
> >  {
> >       struct worker_pool *pool = worker->pool;
> > +     struct work_struct *work = list_first_entry(&pool->worklist,
> > +                                     struct work_struct, entry);
>
> I'm not sure about this. It's depending on an external condition (active
> work item) which isn't obvious and when that condition breaks the resulting
> bug will be one which is difficult to reproduce. Adding to that, pwq isn't
> even the object this code path is interested in, which is the cause of the
> previous problem too.

Ok, I agree with you.

Thanks
Lai