linux-kernel - Re: [patch 1/3] mm: fix pageref leak in do_swap

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Date:	Tue, 21 Apr 2009 14:15:58 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] mm: fix pageref leak in do_swap_page()

* Johannes Weiner <hannes@...xchg.org> [2009-04-21 10:19:03]:

> On Tue, Apr 21, 2009 at 08:44:20AM +0530, Balbir Singh wrote:
> > * Johannes Weiner <hannes@...xchg.org> [2009-04-20 22:24:43]:
> > 
> > > By the time the memory cgroup code is notified about a swapin we
> > > already hold a reference on the fault page.
> > > 
> > > If the cgroup callback fails make sure to unlock AND release the page
> > > or we leak the reference.
> > > 
> > > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > > Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > 
> > Seems reasonable to me, could you make the changelog more verbose and
> > mention that lookup_swap_cache() gets a reference to the page and we
> > need to release the extra reference.
> 
> Okay, I will add that information.
> 

Thanks

> > BTW, have you had any luck reproducing the issue? How did you catch
> > the problem?
> 
> I reviewed all the exit points when I shuffled code around in there
> for another series that uses a lighter version of do_wp_page() for
> swap write-faults.  I never triggered that problem.
>

Good way of catching a problem, play with the code :) 

-- 
	Balbir
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