linux-kernel - Re: [PATCH 2/5] oom: select_bad_process: PF_EXITING check should take ->mm into account

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

Date:	Mon, 31 May 2010 18:43:54 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 2/5] oom: select_bad_process: PF_EXITING check should
	take ->mm into account

Thanks a lot Kosaki for doing this!

I still can't find the time to play with this code :/

On 05/31, KOSAKI Motohiro wrote:
>
> select_bad_process() checks PF_EXITING to detect the task which is going
> to release its memory, but the logic is very wrong.
>
> 	- a single process P with the dead group leader disables
> 	  select_bad_process() completely, it will always return
> 	  ERR_PTR() while P can live forever
>
> 	- if the PF_EXITING task has already released its ->mm
> 	  it doesn't make sense to expect it is goiing to free
> 	  more memory (except task_struct/etc)
>
> Change the code to ignore the PF_EXITING tasks without ->mm.
>
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -287,7 +287,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>  		 * the process of exiting and releasing its resources.
>  		 * Otherwise we could get an easy OOM deadlock.
>  		 */
> -		if (p->flags & PF_EXITING) {
> +		if ((p->flags & PF_EXITING) && p->mm) {

(strictly speaking, this change is needed after 3/5 which removes the
 top-level "if (!p->mm)" check in select_bad_process).


I'd like to add a note... with or without this, we have problems
with the coredump. A thread participating in the coredumping
(group-leader in this case) can have PF_EXITING && mm, but this doesn't
mean it is going to exit soon, and the dumper can use a lot more memory.

Otoh, if select_bad_process() chooses the thread which dumps the core,
SIGKILL can't stop it. This should be fixed in do_coredump() paths, this
is the long-standing problem.

And, as it was already discussed, we only check the group-leader here.
But I can't suggest something better.

Oleg.

--
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/