netdev - Re: [netfilter-core] kernel panic: Out of memory and no killable processes... (2)

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Date:   Mon, 29 Jan 2018 17:57:22 +0100
From:   Florian Westphal <fw@...len.de>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Florian Westphal <fw@...len.de>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        davem@...emloft.net, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        aarcange@...hat.com, yang.s@...baba-inc.com, mhocko@...e.com,
        syzkaller-bugs@...glegroups.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, linux-mm@...ck.org, rientjes@...gle.com,
        akpm@...ux-foundation.org, guro@...com,
        kirill.shutemov@...ux.intel.com
Subject: Re: [netfilter-core] kernel panic: Out of memory and no killable
 processes... (2)

Kirill A. Shutemov <kirill@...temov.name> wrote:
> On Mon, Jan 29, 2018 at 08:23:57AM +0100, Florian Westphal wrote:
> > > vmalloc() once became killable by commit 5d17a73a2ebeb8d1 ("vmalloc: back
> > > off when the current task is killed") but then became unkillable by commit
> > > b8c8a338f75e052d ("Revert "vmalloc: back off when the current task is
> > > killed""). Therefore, we can't handle this problem from MM side.
> > > Please consider adding some limit from networking side.
> > 
> > I don't know what "some limit" would be.  I would prefer if there was
> > a way to supress OOM Killer in first place so we can just -ENOMEM user.
> 
> Just supressing OOM kill is a bad idea. We still leave a way to allocate
> arbitrary large buffer in kernel.

Isn't that what we do everywhere in network stack?

I think we should try to allocate whatever amount of memory is needed
for the given xtables ruleset, given that is what admin requested us to do.

I also would not know what limit is sane -- I've seen setups with as much
as 100k iptables rules, and that was 5 years ago.

And even if we add a "Xk rules" limit, it might be too much for
low-memory systems, or not enough for whatever other use case there
might be.