Re: [patch 1/3] mm: fix pageref leak in do_swap_page()

From: Balbir Singh
Date: Tue Apr 21 2009 - 04:47:17 EST


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

> On Tue, Apr 21, 2009 at 08:44:20AM +0530, Balbir Singh wrote:
> > * Johannes Weiner <hannes@xxxxxxxxxxx> [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@xxxxxxxxxxx>
> > > Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> >
> > 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/