Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754872Ab1C2B1L (ORCPT ); Mon, 28 Mar 2011 21:27:11 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:43437 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752295Ab1C2B1J convert rfc822-to-8bit (ORCPT ); Mon, 28 Mar 2011 21:27:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=PmHbqpZrZ7jBY/JM32CLeyRr6RcXft3RUEtXMZpV9oHEk9ZKDUgHJ+BCGwtJQt7uF1 JuDRl0RmfXDQT1j1S4kabWj1tWDHNgxYxIYyPkIq0t1TixBWCZ1HVXHTgwGGzjBrBwtj 0QPkE39shS8jVcNoaxwLvJDbNMBMAhybaEW9k= MIME-Version: 1.0 In-Reply-To: <20110329101234.54d5d45a.kamezawa.hiroyu@jp.fujitsu.com> References: <20110324182240.5fe56de2.kamezawa.hiroyu@jp.fujitsu.com> <20110324105222.GA2625@barrios-desktop> <20110325090411.56c5e5b2.kamezawa.hiroyu@jp.fujitsu.com> <20110325115453.82a9736d.kamezawa.hiroyu@jp.fujitsu.com> <20110326023452.GA8140@google.com> <20110328162137.GA2904@barrios-desktop> <20110329085033.6e20868e.kamezawa.hiroyu@jp.fujitsu.com> <20110329093257.73357bbc.kamezawa.hiroyu@jp.fujitsu.com> <20110329101234.54d5d45a.kamezawa.hiroyu@jp.fujitsu.com> Date: Tue, 29 Mar 2011 10:27:08 +0900 Message-ID: Subject: Re: [PATCH 0/4] forkbomb killer From: Minchan Kim To: KAMEZAWA Hiroyuki , Andrew Morton Cc: Hiroyuki Kamezawa , Michel Lespinasse , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "rientjes@google.com" , Andrey Vagin , KOSAKI Motohiro , Hugh Dickins , Johannes Weiner , Rik van Riel Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11624 Lines: 266 On Tue, Mar 29, 2011 at 10:12 AM, KAMEZAWA Hiroyuki wrote: > On Tue, 29 Mar 2011 10:12:31 +0900 > Minchan Kim wrote: > >> On Tue, Mar 29, 2011 at 9:32 AM, KAMEZAWA Hiroyuki >> wrote: >> > On Tue, 29 Mar 2011 09:24:30 +0900 >> > Minchan Kim wrote: >> > >> >> On Tue, Mar 29, 2011 at 8:50 AM, KAMEZAWA Hiroyuki >> >> wrote: >> >> > On Tue, 29 Mar 2011 01:21:37 +0900 >> >> > Minchan Kim wrote: >> >> > >> >> >> On Sat, Mar 26, 2011 at 05:48:45PM +0900, Hiroyuki Kamezawa wrote: >> >> >> > 2011/3/26 Michel Lespinasse : >> >> >> > > 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. >> >> >> >> >> >> Hi Kame, >> >> >> >> >> >> I am worried about run-time cost. >> >> >> Should we care of mistake of users for robustness of OS? >> >> >> Mostly right but we can't handle all mistakes of user so we need admin. >> >> >> For exampe, what happens if admin execute "rm -rf /"? >> >> >> For avoiding it, we get a solution "backup" about critical data. >> >> >> >> >> > >> >> > Then, my patch is configurable and has control knobs....never invasive for >> >> > people who don't want it. And simple and very low cost. It will have >> >> > no visible performance/resource usage impact for usual guys. >> >> > >> >> > >> >> > >> >> >> In the same manner, if the system is very critical of forkbomb, >> >> >> admin should consider it using memcg, virtualization, ulimit and so on. >> >> >> If he don't want it, he should become a hard worker who have to >> >> >> cross over other building to reboot it. Although he is a diligent man, >> >> >> Reboot isn't good. So I suggest following patch which is just RFC. >> >> >> For making formal patch, I have to add more comment and modify sysrq.txt. >> >> >> >> >> > >> >> > For me, sysrq is of-no-use as I explained. >> >> >> >> Go to other building and new login? >> >> >> > I cannot login when the system is near happens. >> >> I understand so I said your solution would be a last resort. >> >> > >> >> I think if server is important on such problem, it should have a solution. >> >> The solution can be careful admin step or console with serial for >> >> sysrq step or your forkbomb killer. We have been used sysrq with local >> >> solution of last resort. In such context, sysrq solution ins't bad, I >> >> think. >> >> >> > >> > Mine works with Sysrq-f and this works poorly than mine. >> > >> >> If you can't provide 1 and 2, your forkbomb killer would be a last resort. >> >> But someone can solve the problem in just careful admin or sysrq. >> >> In that case, the user can disable forkbomb killer then it doesn't >> >> affect system performance at all. >> >> So maybe It could be separate topic. >> >> >> >> > >> >> >> From 51bec44086a6b6c0e56ea978a2eb47e995236b47 Mon Sep 17 00:00:00 2001 >> >> >> From: Minchan Kim >> >> >> Date: Tue, 29 Mar 2011 00:52:20 +0900 >> >> >> Subject: [PATCH] [RFC] Prevent livelock by forkbomb >> >> >> >> >> >> Recently, We discussed how to prevent forkbomb. >> >> >> The thing is a trade-off between cost VS effect. >> >> >> >> >> >> Forkbomb is a _race_ case which happes by someone's mistake >> >> >> so if we have to pay cost in fast path(ex, fork, exec, exit), >> >> >> It's a not good. >> >> >> >> >> >> Now, sysrq + I kills all processes. When I tested it, I still >> >> >> need rebooting to work my system really well(ex, x start) >> >> >> although console works. I don't know why we need such sysrq(kill >> >> >> all processes and then what we can do?) >> >> >> >> >> >> So I decide to change sysrq + I to meet our goal which prevent >> >> >> forkbomb. The rationale is following as. >> >> >> >> >> >> Forkbomb means somethings makes repeately tasks in a short time so >> >> >> system don't have a free page then it become almost livelock state. >> >> >> This patch uses the characteristc of forkbomb. >> >> >> >> >> >> When you push sysrq + I, it kills recent created tasks. >> >> >> (In this version, 1 minutes). Maybe all processes included >> >> >> forkbomb tasks are killed. If you can't get normal state of system >> >> >> after you push sysrq + I, you can try one more. It can kill futher >> >> >> recent tasks(ex, 2 minutes). >> >> >> >> >> >> You can continue to do it until your system becomes normal state. >> >> >> >> >> >> Signed-off-by: Minchan Kim >> >> >> --- >> >> >>  drivers/tty/sysrq.c   |   45 ++++++++++++++++++++++++++++++++++++++++++--- >> >> >>  include/linux/sched.h |    6 ++++++ >> >> >>  2 files changed, 48 insertions(+), 3 deletions(-) >> >> >> >> >> >> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c >> >> >> index 81f1395..6fb7e18 100644 >> >> >> --- a/drivers/tty/sysrq.c >> >> >> +++ b/drivers/tty/sysrq.c >> >> >> @@ -329,6 +329,45 @@ static void send_sig_all(int sig) >> >> >>       } >> >> >>  } >> >> >> >> >> >> +static void send_sig_recent(int sig) >> >> >> +{ >> >> >> +     struct task_struct *p; >> >> >> +     unsigned long task_jiffies, last_jiffies = 0; >> >> >> +     bool kill = false; >> >> >> + >> >> >> +retry: >> >> > >> >> > you need tasklist lock for scanning reverse. >> >> >> >> Okay. I will look at it. >> >> >> >> > >> >> >> +     for_each_process_reverse(p) { >> >> >> +             if (p->mm && !is_global_init(p) && !fatal_signal_pending(p)) { >> >> >> +                     /* recent created task */ >> >> >> +                     last_jiffies = timeval_to_jiffies(p->real_start_time); >> >> >> +                     force_sig(sig, p); >> >> >> +                     break; >> >> > >> >> > why break ? you need to kill all youngers. And what is the relationship with below ? >> >> >> >> It's for selecting recent _youngest_ task which are not kthread, not >> >> init, not handled by below loop. In below loop, it start to send KILL >> >> signal processes which are created within 1 minutes from _youngest_ >> >> process creation time. >> >> >> >> > >> >> > >> >> >> +             } >> >> >> +     } >> >> >> + >> >> >> +     for_each_process_reverse(p) { >> >> >> +             if (p->mm && !is_global_init(p)) { >> >> >> +                     task_jiffies = timeval_to_jiffies(p->real_start_time); >> >> >> +                     /* >> >> >> +                      * Kill all processes which are created recenlty >> >> >> +                      * (ex, 1 minutes) >> >> >> +                      */ >> >> >> +                     if (task_jiffies > (last_jiffies - 60 * HZ)) { >> >> >> +                             force_sig(sig, p); >> >> >> +                             kill = true; >> >> >> +                     } >> >> >> +                     else >> >> >> +                             break; >> >> >> +             } >> >> >> +     } >> >> >> + >> >> >> +     /* >> >> >> +      * If we can't kill anything, restart with next group. >> >> >> +      */ >> >> >> +     if (!kill) >> >> >> +             goto retry; >> >> >> +} >> >> > >> >> > This is not useful under OOM situation, we cannot use 'jiffies' to find younger tasks >> >> > because "memory reclaim-> livelock" can take some amount of minutes very easily. >> >> > So, I used other metrics. I think you do the same mistake I made before, >> >> > this doesn't work. >> >> >> >> As far as I understand right, p->real_start_time is create time, not jiffies. >> >> What I want is that kill all processes created recently, not all >> >> process like old sysrq + I. >> >> >> >> Am I miss something? >> >> >> > When you run 'make -j' or 'Andrey's case' with "swap". You'll see 1minutes is too >> > short and no task will be killed. >> > >> > To determine this 60*HZ is diffuclut. I think no one cannot detemine this. >> > 1 minute is too short, 10 minutes are too long. So, I used a different manner, >> > which seems to work well. >> >> Okay. I can handle it. How about this? >> >> retry: >> old_time = yougest_task->start_time; >> for_each_process_reverse(p) { >>       time = p->start_time; >>       if (time > old_time - 60 * HZ) >>               kill(p); >> } >> >> /* >>  * If user push sysrq within 1 minutes from last again, >>  * we kill processes more. >>  */ >> if (call_time < (now - 60 * HZ)) >>       goto retry; >> >> call_time = now; >> return; >> >> So whenever user push sysrq, older tasks would be killed and at last, >> root forkbomb task would be killed. >> > > Maybe good for a single user system and it can send Sysrq. > But I myself not very excited with this new feature becasuse I need to > run to push Sysrq .... > > Please do as you like, I think the idea itself is interesting. > But I love some automatic ones. I do other jobs. Okay. Thanks for the comment, Kame. I hope Andrew or someone gives feedback forkbomb problem itself before diving into this. -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/