Messages in this thread | | | Date | Tue, 14 Apr 2020 13:05:16 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] seqlock: Use while instead of if+goto in __read_seqcount_begin |
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On Fri, Apr 10, 2020 at 12:56:58PM +0100, Will Deacon 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@bytedance.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.
Linus sometimes prefers the goto variant as that better expresses the exception model. But like Will, I don't particularly care. That said, Will, would it make sense to use smp_cond_load_relaxed() here ?
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