netdev - Re: struct pid memory leak

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Date:	Sat, 23 Jan 2016 11:50:14 -0800
From:	Eric Dumazet <edumazet@...gle.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Willy Tarreau <w@....eu>, 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>,
	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 10:46 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> 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.

Note that kmemleak is not needed.

Just run a normal kernel (eventually using slab_nomerge=1 boot cmd to
make sure 'pid' slab is not shared)

It seems that bug is rather old, as linux-4.0 has it.