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

[Zqiang]

On 2021/10/26 下午10:47, Jens Axboe wrote:
> On 10/26/21 4:32 AM, Muchun Song wrote:
> > On Tue, Oct 26, 2021 at 11:23 AM Zqiang <qiang.zhang1211@xxxxxxxxx> 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@xxxxxxxxx>
> > > ---
> > >   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. */
> Note that it's a raw spinlock. Honestly I'd probably prefer if we just leave
> it as-is. There are plans to improve the io-wq locking, and a rcu lock/unlock
> is pretty cheap.
>
> That said, if resend with a comment fully detailing why it's OK currently,
> then I'd be fine with that as well.
Thanks Jens Axboe, Muchun

 I  will  add a comment fully detailing and resend.