linux-kernel - Re: [PATCH 03/24] workqueue: Not all work insertion needs to wake up a worker

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Message-ID: <CAJhGHyCdgfNY83ddpQRpsCVvPQF9HtuNXXFFbpJuxYLL+mYcZQ@mail.gmail.com>
Date:   Tue, 23 May 2023 17:54:10 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     torvalds@...ux-foundation.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com,
        joshdon@...gle.com, brho@...gle.com, briannorris@...omium.org,
        nhuck@...gle.com, agk@...hat.com, snitzer@...nel.org,
        void@...ifault.com
Subject: Re: [PATCH 03/24] workqueue: Not all work insertion needs to wake up
 a worker

On Fri, May 19, 2023 at 8:17 AM Tejun Heo <tj@...nel.org> wrote:

> +       pool = pwq->pool;
> +
>         /*
>          * If @work was previously on a different pool, it might still be
>          * running there, in which case the work needs to be queued on that
>          * pool to guarantee non-reentrancy.
>          */
>         last_pool = get_work_pool(work);
> -       if (last_pool && last_pool != pwq->pool) {
> +       if (last_pool && last_pool != pool) {
>                 struct worker *worker;
>
>                 raw_spin_lock(&last_pool->lock);
> @@ -1638,13 +1636,14 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
>
>                 if (worker && worker->current_pwq->wq == wq) {
>                         pwq = worker->current_pwq;
> +                       pool = pwq->pool;

The code above does a "raw_spin_lock(&last_pool->lock);", and
the code next does a "raw_spin_unlock(&pool->lock);".

                            WARN_ON_ONCE(pool != last_pool);

can be added here and served as a comment.

>                 } else {
>                         /* meh... not running there, queue here */
>                         raw_spin_unlock(&last_pool->lock);
> -                       raw_spin_lock(&pwq->pool->lock);
> +                       raw_spin_lock(&pool->lock);
>                 }
>         } else {
> -               raw_spin_lock(&pwq->pool->lock);
> +               raw_spin_lock(&pool->lock);
>         }
>