Messages in this thread | | | Date | Tue, 14 Apr 2020 14:48:31 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] seqlock: Use while instead of if+goto in __read_seqcount_begin |
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On Tue, Apr 14, 2020 at 01:05:16PM +0200, Peter Zijlstra wrote: > 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 ?
Oh yeah, good thinking. Didn't spot that one, but it should work well as long as smp_cond_load_relaxed() always implies a control dependency (surely it has to?)
Will
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