linux-kernel - Re: [External] Re: [PATCH] seqlock: Use while instead of if+goto in __read_seqcount

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Message-ID: <CAMZfGtURunxwwGHM+5J-A605y=Ww=jQsxCF173mgQFQ=ySVV0A@mail.gmail.com>
Date:   Tue, 14 Apr 2020 16:58:55 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     peterz@...radead.org
Cc:     mingo@...hat.com, Will Deacon <will@...nel.org>, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] seqlock: Use while instead of if+goto in __read_seqcount_begin

On Fri, Apr 10, 2020 at 7:57 PM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Apr 09, 2020 at 09:45:58PM +0800, Muchun Song wrote:
> > The creators of the C language gave us the while keyword. Let's use
> > that instead of synthesizing it from if+goto.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > ---
> >  include/linux/seqlock.h | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> >
> > diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> > index 8b97204f35a77..7bdea019814ce 100644
> > --- a/include/linux/seqlock.h
> > +++ b/include/linux/seqlock.h
> > @@ -125,12 +125,8 @@ static inline unsigned __read_seqcount_begin(const seqcount_t *s)
> >  {
> >       unsigned ret;
> >
> > -repeat:
> > -     ret = READ_ONCE(s->sequence);
> > -     if (unlikely(ret & 1)) {
> > +     while (unlikely((ret = READ_ONCE(s->sequence)) & 1))
> >               cpu_relax();
> > -             goto repeat;
> > -     }
> >       kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
> >       return ret;
>
> Patch looks fine to me, but I'll leave it to Peter as I don't have a
> preference either way.
>

This patch can make the code look simple and easy to read.
What is your opinion, Peter? Thanks.


-- 
Yours,
Muchun