linux-kernel - Re: [PATCH 0/4] forkbomb killer

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Date:	Sat, 26 Mar 2011 17:48:45 +0900
From:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 0/4] forkbomb killer

2011/3/26 Michel Lespinasse <walken@...gle.com>:
> On Fri, Mar 25, 2011 at 01:05:50PM +0900, Minchan Kim wrote:
>> Okay. Each approach has a pros and cons and at least, now anyone
>> doesn't provide any method and comments but I agree it is needed(ex,
>> careless and lazy admin could need it strongly). Let us wait a little
>> bit more. Maybe google guys or redhat/suse guys would have a opinion.
>
> I haven't heard of fork bombs being an issue for us (and it's not been
> for me on my desktop, either).
>
> Also, I want to point out that there is a classical userspace solution
> for this, as implemented by killall5 for example. One can do
> kill(-1, SIGSTOP) to stop all processes that they can send
> signals to (except for init and itself). Target processes
> can never catch or ignore the SIGSTOP. This stops the fork bomb
> from causing further damage. Then, one can look at the process
> tree and do whatever is appropriate - including killing by uid,
> by cgroup or whatever policies one wants to implement in userspace.
> Finally, the remaining processes can be restarted using SIGCONT.
>

Can that solution work even under OOM situation without new login/commands ?
Please show us your solution, how to avoid Andrey's Bomb  with your way.
Then, we can add Documentation, at least. Or you can show us your tool.

Maybe it is....
- running as a daemon. (because it has to lock its work memory before OOM.)
- mlockall its own memory to work under OOM.
- It can show process tree of users/admin or do all in automatic way
with user's policy.
- tell us which process is guilty.
- wakes up automatically when OOM happens.....IOW, OOM should have some notifier
  to userland.
- never allocate any memory at running. (maybe it can't use libc.)
- never be blocked by any locks, for example, some other task's mmap_sem.
  One of typical mistakes of admins at OOM is typing 'ps' to see what
happens.....
- Can be used even with GUI system, which can't show console.

Thanks,
-Kame
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