linux-kernel - Re: uprobes: memory leak in enable/disable loop

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Date:	Tue, 16 Aug 2016 16:37:10 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Brenden Blanco <bblanco@...mgrid.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: uprobes: memory leak in enable/disable loop

On Tue 16-08-16 16:25:12, Oleg Nesterov wrote:
> On 08/16, Oleg Nesterov wrote:
> >
> > On 08/15, Brenden Blanco wrote:
> > >
> > > Hi folks,
> > >
> > > I think I have come across a memory leak in uprobes, which is fairly easy to
> > > reproduce.
> >
> > At first glance this looks as a problem in memcg, add CC's...
> >
> > put_page(old_page) looks properly balanced, and I assume we do not need
> > the additional "uncharge", we can rely on __page_cache_release().
> >
> > And I do not see any leak if I try to reproduce with CONFIG_MEMCG=n.
> 
> Heh. it seems that mem_cgroup_*() logic was always wrong in __replace_page().

Yes this seems broken since 00501b531c47 ("mm: memcontrol: rewrite
charge API")

> Could you try the patch below?

The patch looks good to me. Thanks!

> Oleg.
> ---
> 
> --- x/kernel/events/uprobes.c
> +++ x/kernel/events/uprobes.c
> @@ -200,7 +200,8 @@ static int __replace_page(struct vm_area
>  
>  	err = 0;
>   unlock:
> -	mem_cgroup_cancel_charge(kpage, memcg, false);
> + 	if (err)
> +		mem_cgroup_cancel_charge(kpage, memcg, false);
>  	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
>  	unlock_page(page);
>  	return err;

-- 
Michal Hocko
SUSE Labs