Date: Wed, 15 May 2013 02:00:53 -0700
From: Kent Overstreet <koverstreet@google.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
        akpm@linux-foundation.org, Zach Brown <zab@redhat.com>,
        Felipe Balbi <balbi@ti.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mark Fasheh <mfasheh@suse.com>, Joel Becker <jlbec@evilplan.org>,
        Rusty Russell <rusty@rustcorp.com.au>, Jens Axboe <axboe@kernel.dk>,
        Asai Thambi S P <asamymuthupa@micron.com>,
        Selvan Mani <smani@micron.com>, Sam Bradshaw <sbradshaw@micron.com>,
        Jeff Moyer <jmoyer@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Benjamin LaHaise <bcrl@kvack.org>,
        Christoph Lameter <cl@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 04/21] Generic percpu refcounting
Message-ID: <20130515090053.GC16164@moria.home.lan>
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 <20130514152836.GA21972@redhat.com>
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On Tue, May 14, 2013 at 05:28:36PM +0200, Oleg Nesterov wrote:
> On 05/14, Tejun Heo wrote:
> >
> > > +int percpu_ref_tryget(struct percpu_ref *ref)
> > > +{
> > > +	int ret = 1;
> > > +
> > > +	preempt_disable();
> > > +
> > > +	if (!percpu_ref_dead(ref))
> > > +		percpu_ref_get(ref);
> > > +	else
> > > +		ret = 0;
> > > +
> > > +	preempt_enable();
> > > +
> > > +	return ret;
> > > +}
> ...
> > BTW, why is this
> > function necessary?  What's the use case?
> 
> Yes, I was wondering too.
> 
> And please note that this code _looks_ wrong, percpu_ref_get() still
> can increment ref->count.

Yeah I see what you mean, I changed how ret is set.

But also splitting tryget() and count() out into another patch to go
with the module conversion.

> Hmm. Just noticed this comment above percpu_ref_kill()
> 
> 	* The caller must issue a synchronize_rcu()/call_rcu() before calling
> 	* percpu_ref_put() to drop the initial ref.
> 
> Really?

That's also left over from the dynamic version, whoops.
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