linux-kernel - Re: [PATCH -mm -repost] memcg: do not hang on OOM when killed by userspace OOM access to memory reserves

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.02.1404231627410.11506@chino.kir.corp.google.com>
Date:	Wed, 23 Apr 2014 16:28:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH -mm -repost] memcg: do not hang on OOM when killed by
 userspace OOM access to memory reserves

On Wed, 23 Apr 2014, Michal Hocko wrote:

> Eric has reported that he can see task(s) stuck in memcg OOM handler
> regularly.  The only way out is to
> 
> 	echo 0 > $GROUP/memory.oom_controll
> 
> His usecase is:
> 
> - Setup a hierarchy with memory and the freezer (disable kernel oom and
>   have a process watch for oom).
> 
> - In that memory cgroup add a process with one thread per cpu.
> 
> - In one thread slowly allocate once per second I think it is 16M of ram
>   and mlock and dirty it (just to force the pages into ram and stay
>   there).
> 
> - When oom is achieved loop:
>   * attempt to freeze all of the tasks.
>   * if frozen send every task SIGKILL, unfreeze, remove the directory in
>     cgroupfs.
> 
> Eric has then pinpointed the issue to be memcg specific.
> 
> All tasks are sitting on the memcg_oom_waitq when memcg oom is disabled.
> Those that have received fatal signal will bypass the charge and should
> continue on their way out.  The tricky part is that the exit path might
> trigger a page fault (e.g.  exit_robust_list), thus the memcg charge,
> while its memcg is still under OOM because nobody has released any charges
> yet.
> 
> Unlike with the in-kernel OOM handler the exiting task doesn't get
> TIF_MEMDIE set so it doesn't shortcut further charges of the killed task
> and falls to the memcg OOM again without any way out of it as there are no
> fatal signals pending anymore.
> 
> This patch fixes the issue by checking PF_EXITING early in
> mem_cgroup_try_charge and bypass the charge same as if it had fatal
> signal pending or TIF_MEMDIE set.
> 
> Normally exiting tasks (aka not killed) will bypass the charge now but
> this should be OK as the task is leaving and will release memory and
> increasing the memory pressure just to release it in a moment seems
> dubious wasting of cycles.  Besides that charges after exit_signals should
> be rare.
> 
> Reported-by: Eric W. Biederman <ebiederm@...ssion.com>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: David Rientjes <rientjes@...gle.com>

I think we should wait for a Tested-by from Eric if this is going to be 
backported to stable, though, to meet the criteria.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/