linux-kernel - Re: [PATCH v1 3/5] seqlock: seqcount_t: Implement all read APIs as statement expressions

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Message-ID: <20200828083702.GA7074@lx-t490>
Date:   Fri, 28 Aug 2020 10:37:02 +0200
From:   "Ahmed S. Darwish" <a.darwish@...utronix.de>
To:     peterz@...radead.org
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/5] seqlock: seqcount_t: Implement all read APIs as
 statement expressions

On Fri, Aug 28, 2020 at 10:30:22AM +0200, peterz@...radead.org wrote:
> On Fri, Aug 28, 2020 at 03:07:08AM +0200, Ahmed S. Darwish wrote:
> >  #define __read_seqcount_begin(s)					\
> > +({									\
> > +	unsigned seq;							\
> > +									\
> > +	do {								\
> > +		seq = __seqcount_sequence(s);				\
> > +		if (likely(! (seq & 1)))				\
> > +			break;						\
> > +		cpu_relax();						\
> > +	} while (true);							\
> > +									\
> > +	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);			\
> > +	seq;								\
> > +})
>
> Since we're there anyway, does it make sense to (re)write this like:
>
> 	while ((seq = __seqcount_sequence(s)) & 1)
> 		cpu_relax();
>
> ?
>

Yeah, much better of course; will do.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH