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    SubjectRe: [PATCH 0/4] forkbomb killer
    On Thu, 24 Mar 2011 19:52:22 +0900
    Minchan Kim <> wrote:

    > Hi Kame,

    > On Thu, Mar 24, 2011 at 06:22:40PM +0900, KAMEZAWA Hiroyuki wrote:
    > >
    > > I tested with several forkbomb cases and this patch seems work fine.
    > >
    > > Maybe some more 'heuristics' can be added....but I think this simple
    > > one works enough. Any comments are welcome.
    > Sorry for the late review. Recently I dont' have enough time to review patches.
    > Even I didn't start to review this series but I want to review this series.
    > It's one of my interest features. :)
    > But before digging in code, I would like to make a consensus to others to
    > need this feature. Let's Cc others.
    > What I think is that about "cost(frequent case) VS effectiveness(very rare case)"
    > as you expected. :)
    > 1. At least, I don't meet any fork-bomb case for a few years. My primary linux usage
    > is just desktop and developement enviroment, NOT server. Only thing I have seen is
    > just ltp or intentional fork-bomb test like hackbench. AFAIR, ltp case was fixed
    > a few years ago. Although it happens suddenly, reboot in desktop isn't critical
    > as much as server's one.

    Personally, I've met forkbombs several times by typing "make -j" mistake.

    I met a forkbomb on production system by buggy script, once.
    That happens because
    1. $PATH includes "."
    2. a programmer write a scirpt "date" and call "date" in the script.

    Maybe this is a one of typical case of forkbomb. I needed to dig crashdump to find
    fragile of page-caches and see what happens...But, I guess, if appearent forkbomb
    happens, the issue will not be sent to my team because we're 2nd line support team
    and 1st line should block it ;).

    So, I'm not sure how many forkbombs happens in server world in a year. But I guess
    forkbomb still happens in many development systems because there is no guard
    against it.

    > 2. I don't know server enviroment but I think applications executing on server
    > are selected by admin carefully. So virus program like fork-bomb is unlikely in there.
    > (Maybe I am wrong. You know than me).
    > If some normal program becomes fork-bomb unexpectedly, it's critical.
    > Admin should select application with much testing very carefully. But I don't know
    > the reality. :(

    Yes, admin selects applications carefully. There is no 100% protection by human's hand.

    > Of course, although he did such efforts, he could meet OOM hang situation.
    > In the case, he can't avoid rebooting. Sad. But for helping him, should we pay cost
    > in normal situation?(Again said, I didn't start looking at your code so
    > I can't expect the cost but at least it's more than as-is).
    > It could help developing many virus program and to make careless admins.
    > It's just my private opinion.
    > I don't have enough experience so I hope listen other's opinions
    > about generic fork-bomb killer, not memcg.
    > I don't intend to ignore your effort but justify your and my effort rightly.

    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.


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