Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 28 Aug 2020 10:37:02 +0200
From:   "Ahmed S. Darwish" <a.darwish@linutronix.de>
To:     peterz@infradead.org
Cc:     Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Sebastian A. Siewior" <bigeasy@linutronix.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 3/5] seqlock: seqcount_t: Implement all read APIs as
 statement expressions
Message-ID: <20200828083702.GA7074@lx-t490>
References: <20200519214547.352050-1-a.darwish@linutronix.de>
 <20200828010710.5407-1-a.darwish@linutronix.de>
 <20200828010710.5407-4-a.darwish@linutronix.de>
 <20200828083022.GO1362448@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200828083022.GO1362448@hirez.programming.kicks-ass.net>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 28, 2020 at 10:30:22AM +0200, peterz@infradead.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