linux-kernel - Re: [PATCH, RFC] percpu_counters: make fbc->count read atomic on 32 bit architecture

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Message-Id: <1223400140.26330.76.camel@lappy.programming.kicks-ass.net>
Date:	Tue, 07 Oct 2008 19:22:20 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	richard kennedy <richard@....demon.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH, RFC] percpu_counters: make fbc->count read atomic on
	32 bit architecture

On Tue, 2008-10-07 at 18:09 +0100, richard kennedy wrote:
> Peter Zijlstra wrote:
> .....
> > +static inline int atomic64_dec_and_test(atomic64_t *v)
> > +{
> > +	int ret;
> > +
> > +	write_seqlock(&v->slock);
> > +	v->counter--;
> > +	ret = !v->counter;
> > +	write_sequnlock(&v->slock);
> > +
> > +	return ret;
> > +}
> > +
> > +static inline int atomic64_add_and_test(atomic64_t *v)
> > +{
> > +	int ret;
> > +
> > +	write_seqlock(&v->slock);
> > +	v->counter++;
> > +	ret = !v->counter;
> > +	write_sequnlock(&v->slock);
> > +
> > +	return ret;
> > +}
> would it be more logical to call this atomic64_inc_and_test to match the
> above dec_and_test ?

Yeah, I know of at least 2 other bugs in here, but I wanted some real
early feedback :-)

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