Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752974Ab1C2Ajb (ORCPT ); Mon, 28 Mar 2011 20:39:31 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:43014 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752231Ab1C2Aj3 (ORCPT ); Mon, 28 Mar 2011 20:39:29 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 29 Mar 2011 09:32:57 +0900 From: KAMEZAWA Hiroyuki To: Minchan Kim 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 Subject: Re: [PATCH 0/4] forkbomb killer Message-Id: <20110329093257.73357bbc.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: 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> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.1.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 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: 9455 Lines: 223 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 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. Thanks, -Kmae -- 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/