linux-kernel - Re: struct pid memory leak

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Date:	Sat, 23 Jan 2016 19:46:45 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Willy Tarreau <w@....eu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Eric Dumazet <edumazet@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: struct pid memory leak

On Sat, Jan 23, 2016 at 7:40 PM, Willy Tarreau <w@....eu> wrote:
> On Sat, Jan 23, 2016 at 07:14:33PM +0100, Dmitry Vyukov wrote:
>> I've attached my .config.
>> Also run this program in a parallel loop. I think it's leaking not
>> every time, probably some race is involved.
>
> Thank you. Just in order to confirm, am I supposed to see the
> messages you quoted in dmesg ?


I think the simplest way to confirm that you can reproduce it locally
is to check /proc/slabinfo. When I run this program in a parallel
loop, number of objects in pid cache was constantly growing:

# cat /proc/slabinfo | grep pid
pid                  297    532    576   28    4 : tunables    0    0
  0 : slabdata     19     19      0
...
pid                  412    532    576   28    4 : tunables    0    0
  0 : slabdata     19     19      0
...
pid                 1107   1176    576   28    4 : tunables    0    0
  0 : slabdata     42     42      0
...
pid                 1545   1652    576   28    4 : tunables    0    0
  0 : slabdata     59     59      0


If you want to use kmemleak, then you need to run this program in a
parallel loop for some time, then stop it and then:

$ echo scan > /sys/kernel/debug/kmemleak
$ cat /sys/kernel/debug/kmemleak

If kmemleak has detected any leaks, cat will show them. I noticed that
kmemleak can delay leaks with significant delay, so usually I do scan
at least 5 times.