linux-kernel - Re: [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section

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Message-ID: <CAMZfGtUXq=nQyijktRaP7xp=sAmVCryTjU4Jo5Z=ufed8arnKQ@mail.gmail.com>
Date:   Tue, 26 Oct 2021 18:32:38 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Zqiang <qiang.zhang1211@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, asml.silence@...il.com,
        io-uring@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw
 spinlock critical section

On Tue, Oct 26, 2021 at 11:23 AM Zqiang <qiang.zhang1211@...il.com> wrote:
>
> Due to raw_spin_lock/unlock() contains preempt_disable/enable() action,
> already regarded as RCU critical region, so remove unnecessary
> rcu_read_lock/unlock().
>
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
> ---
>  fs/io-wq.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index cd88602e2e81..401be005d089 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -855,9 +855,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
>         io_wqe_insert_work(wqe, work);
>         clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
>
> -       rcu_read_lock();

Add a comment like:
/* spin_lock can serve as an RCU read-side critical section. */

With that.

Reviewed-by: Muchun Song <songmuchun@...edance.com>

Thanks.

>         do_create = !io_wqe_activate_free_worker(wqe, acct);
> -       rcu_read_unlock();
>
>         raw_spin_unlock(&wqe->lock);
>
> --
> 2.17.1
>