linux-kernel - Re: [PATCH 01/11] blkcg: fix blkg

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Message-ID: <20120427142757.GI27486@google.com>
Date:	Fri, 27 Apr 2012 07:27:57 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	containers@...ts.linux-foundation.org, fengguang.wu@...el.com,
	hughd@...gle.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 01/11] blkcg: fix blkg_alloc() failure path

On Fri, Apr 27, 2012 at 10:26:52AM -0400, Vivek Goyal wrote:
> On Thu, Apr 26, 2012 at 02:59:11PM -0700, Tejun Heo wrote:
> > When policy data allocation fails in the middle, blkg_alloc() invokes
> > blkg_free() to destroy the half constructed blkg.  This ends up
> > calling pd_exit_fn() on policy datas which didn't go through
> > pd_init_fn().  Fix it by making blkg_alloc() call pd_init_fn()
> > immediately after each policy data allocation.
> > 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Cc: Vivek Goyal <vgoyal@...hat.com>
> > ---
> >  block/blk-cgroup.c |    6 +-----
> >  1 files changed, 1 insertions(+), 5 deletions(-)
> > 
> > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> > index 02cf633..4ab7420 100644
> > --- a/block/blk-cgroup.c
> > +++ b/block/blk-cgroup.c
> > @@ -125,12 +125,8 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q)
> >  
> >  		blkg->pd[i] = pd;
> >  		pd->blkg = blkg;
> > -	}
> > -
> > -	/* invoke per-policy init */
> > -	for (i = 0; i < BLKCG_MAX_POLS; i++) {
> > -		struct blkcg_policy *pol = blkcg_policy[i];
> >  
> > +		/* invoke per-policy init */
> >  		if (blkcg_policy_enabled(blkg->q, pol))
> >  			pol->pd_init_fn(blkg);
> 
> Deja Vu. In one of the mails I had said that how about moving init_fn
> in upper loop and get rid of for loop below. Then retracted it saying
> probably you wanted to allocate all the groups first before calling 
> init functions of individual policies. Here we are back again for a
> different reason though. :-)

Heh, yeah, should have updated it then. :)

-- 
tejun
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