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

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Date:	Tue, 16 Aug 2016 16:34:08 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Brenden Blanco <bblanco@...mgrid.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	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 08/16, 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, it seems this was broken by 00501b53 "mm: memcontrol: rewrite charge API".

> Could you try the patch below?

Please see v2 below. We don't need "cancel_charge" under "unlock:" at all.

Johannes, could you review?

Oleg.
---
--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -172,8 +172,10 @@ static int __replace_page(struct vm_area
 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 	err = -EAGAIN;
 	ptep = page_check_address(page, mm, addr, &ptl, 0);
-	if (!ptep)
+	if (!ptep) {
+		mem_cgroup_cancel_charge(kpage, memcg, false);
 		goto unlock;
+	}
 
 	get_page(kpage);
 	page_add_new_anon_rmap(kpage, vma, addr, false);
@@ -200,7 +202,6 @@ static int __replace_page(struct vm_area
 
 	err = 0;
  unlock:
-	mem_cgroup_cancel_charge(kpage, memcg, false);
 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 	unlock_page(page);
 	return err;