linux-kernel - Re: [PATCH 10/13] block, cfq: unlink cfq_io

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Message-ID: <20111026203846.GG355@redhat.com>
Date:	Wed, 26 Oct 2011 16:38:46 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/13] block, cfq: unlink cfq_io_context's immediately

On Wed, Oct 26, 2011 at 12:55:06PM -0700, Tejun Heo wrote:
> Hello,
> 
> On Wed, Oct 26, 2011 at 03:48:57PM -0400, Vivek Goyal wrote:
> > > +		ioc_release_depth_inc(cic->q);
> > > +		cic->exit(cic);
> > > +		cic->release(cic);
> > > +		ioc_release_depth_dec(cic->q);
> > 
> > cic->release(cic) can free the cic? Are we accessing cic after freeing it
> > up in ioc_release_depth_dec(cic->q);
> 
> As cic is RCU freed and we're running w/ irq disabled, this shouldn't
> blow up, but yeah, I'll update it to use local variable instead.

Tejun,

So the only reason that cic needs to be rcu protected because in
cfq_cic_lookup() we can access ioc->ioc_data which can point to a 
cic which is not ours and we are not holding queue lock for that and
we can't access cic->q ?

Rest of the places we are either holding ioc_lock or accessing our
own cic under associated queue lock so it should be safe?

I am wondering if there should be a small text file explaining all
the locking in this area.

Good to see that you are cleaning it all up.

Thanks
Vivek
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