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

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Date:	Fri, 25 Mar 2011 13:05:50 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"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

On Fri, Mar 25, 2011 at 11:54 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Fri, 25 Mar 2011 11:38:19 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> On Fri, Mar 25, 2011 at 9:04 AM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@...fujitsu.com> wrote:
>> > On Thu, 24 Mar 2011 19:52:22 +0900
>> > Minchan Kim <minchan.kim@...il.com> wrote:
>> > To me, the fact "the system _can_ be broken by a normal user program" is the most
>> > terrible thing. With Andrey's case or make -j, a user doesn't need to be an admin.
>> > I believe it's worth to pay costs.
>> > (and I made this function configurable and can be turned off by sysfs.)
>> >
>> > And while testing Andrey's case, I used KVM finaly becasue cost of rebooting was small.
>> > My development server is on other building and I need to push server's button
>> > to reboot it when forkbomb happens ;)
>> > In some environement, cost of rebooting is not small even if it's a development system.
>> >
>>
>> Forkbomb is very rare case in normal situation but if it happens, the
>> cost like reboot would be big. So we need the such facility. I agree.
>> (But I don't know why others don't have a interest if it is important
>> task. Maybe they are so busy due to rc1)
>> Just a concern is cost.
>
> me, too.
>
>> The approach is we can enhance your approach to minimize the cost but
>> apparently it would have a limitation.
>>
> agreed. "tracking" always costs.
>
>> Other approach is we can provide new rescue facility.
>> What I have thought is new sysrq about killing fork-bomb.
>>
> Mine works fine with Sysrq+f. But, I need to go to other building
> for pushing Sysrq.....
>
>> If we execute the new sysrq, the kernel freezes all tasks so forkbomb
>> can't execute any more and kernel ready to receive the command to show
>> the system state. Admin can investigate which is fork-bomb and then he
>> kill the tasks. At last, admin restarts all processes with new sysrq
>> and processes which received SIGKILL start to die.
>>
>> This approach offloads kernel's heuristic forkbomb detection to admin
>> and avoid runtime cost in normal situation.
>> I don't have any code to implement above the concept so it might be ridiculous.
>>
>> What do you think about it?
>>
> For usual user, forkbmob killer works better, rather than special console for
> fatal system.
>
> I can think of 2 similar works. One is Windows's TaskManager. You can kill tasks
> with it (and I guess TaskManager is always on memory...) Another one is
> "guarantee" or "preserve XXXX for special apps." which clustering guys wants for
> quick server failover.
>
> If trouble happens,
>  - freeze all apps other than HA apps.
>  - open the gate for hidden preserved resources (of memory / disks)
>  - do safe failover to other server.
>  - do necessary jobs and reboot.
>
> So, you need to preserve some resources for recover...IOW, have to pay costs.
>
> BTW, Sysrq/TaskManager/Failover doesn't help me, using development system via network.

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.

Regardless of them, I will review series when I have rest time.
Thanks, Kame.

-- 
Kind regards,
Minchan Kim
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