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Date: Tue, 16 Aug 2016 16:25:12 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Brenden Blanco <bblanco@plumgrid.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: uprobes: memory leak in enable/disable loop
Message-ID: <20160816142511.GB17006@redhat.com>
References: <20160815205810.GA22619@gmail.com> <20160816141350.GA17006@redhat.com>
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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().

Could you try the patch below?

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;