Re: [PATCH for 3.2] memcg: do not trap chargers with full callstackon OOM

From: Michal Hocko
Date: Mon Jul 15 2013 - 12:00:16 EST

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In reply to: Michal Hocko: "Re: [PATCH for 3.2] memcg: do not trap chargers with full callstackon OOM"
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On Mon 15-07-13 17:41:19, Michal Hocko wrote:
> On Sun 14-07-13 01:51:12, azurIt wrote:
> > > CC: "Johannes Weiner" <hannes@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, "cgroups mailinglist" <cgroups@xxxxxxxxxxxxxxx>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx>, righi.andrea@xxxxxxxxx
> > >> CC: "Johannes Weiner" <hannes@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, "cgroups mailinglist" <cgroups@xxxxxxxxxxxxxxx>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx>, righi.andrea@xxxxxxxxx
> > >>On Wed 10-07-13 18:25:06, azurIt wrote:
> > >>> >> Now i realized that i forgot to remove UID from that cgroup before
> > >>> >> trying to remove it, so cgroup cannot be removed anyway (we are using
> > >>> >> third party cgroup called cgroup-uid from Andrea Righi, which is able
> > >>> >> to associate all user's processes with target cgroup). Look here for
> > >>> >> cgroup-uid patch:
> > >>> >> https://www.develer.com/~arighi/linux/patches/cgroup-uid/cgroup-uid-v8.patch
> > >>> >>
> > >>> >> ANYWAY, i'm 101% sure that 'tasks' file was empty and 'under_oom' was
> > >>> >> permanently '1'.
> > >>> >
> > >>> >This is really strange. Could you post the whole diff against stable
> > >>> >tree you are using (except for grsecurity stuff and the above cgroup-uid
> > >>> >patch)?
> > >>>
> > >>>
> > >>> Here are all patches which i applied to kernel 3.2.48 in my last test:
> > >>> http://watchdog.sk/lkml/patches3/
> > >>
> > >>The two patches from Johannes seem correct.
> > >>
> > >>From a quick look even grsecurity patchset shouldn't interfere as it
> > >>doesn't seem to put any code between handle_mm_fault and mm_fault_error
> > >>and there also doesn't seem to be any new handle_mm_fault call sites.
> > >>
> > >>But I cannot tell there aren't other code paths which would lead to a
> > >>memcg charge, thus oom, without proper FAULT_FLAG_KERNEL handling.
> > >
> > >
> > >Michal,
> > >
> > >now i can definitely confirm that problem with unremovable cgroups
> > >persists. What info do you need from me? I applied also your little
> > >'WARN_ON' patch.
> >
> > Ok, i think you want this:
> > http://watchdog.sk/lkml/kern4.log
>
> Jul 14 01:11:39 server01 kernel: [ 593.589087] [ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name
> Jul 14 01:11:39 server01 kernel: [ 593.589451] [12021] 1333 12021 172027 64723 4 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.589647] [12030] 1333 12030 172030 64748 2 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.589836] [12031] 1333 12031 172030 64749 3 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590025] [12032] 1333 12032 170619 63428 3 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590213] [12033] 1333 12033 167934 60524 2 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590401] [12034] 1333 12034 170747 63496 4 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590588] [12035] 1333 12035 169659 62451 1 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590776] [12036] 1333 12036 167614 60384 3 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.590984] [12037] 1333 12037 166342 58964 3 0 0 apache2
> Jul 14 01:11:39 server01 kernel: [ 593.591178] Memory cgroup out of memory: Kill process 12021 (apache2) score 847 or sacrifice child
> Jul 14 01:11:39 server01 kernel: [ 593.591370] Killed process 12021 (apache2) total-vm:688108kB, anon-rss:255472kB, file-rss:3420kB
> Jul 14 01:11:41 server01 kernel: [ 595.392920] ------------[ cut here ]------------
> Jul 14 01:11:41 server01 kernel: [ 595.393096] WARNING: at kernel/exit.c:888 do_exit+0x7d0/0x870()
> Jul 14 01:11:41 server01 kernel: [ 595.393256] Hardware name: S5000VSA
> Jul 14 01:11:41 server01 kernel: [ 595.393415] Pid: 12037, comm: apache2 Not tainted 3.2.48-grsec #1
> Jul 14 01:11:41 server01 kernel: [ 595.393577] Call Trace:
> Jul 14 01:11:41 server01 kernel: [ 595.393737] [<ffffffff8105520a>] warn_slowpath_common+0x7a/0xb0
> Jul 14 01:11:41 server01 kernel: [ 595.393903] [<ffffffff8105525a>] warn_slowpath_null+0x1a/0x20
> Jul 14 01:11:41 server01 kernel: [ 595.394068] [<ffffffff81059c50>] do_exit+0x7d0/0x870
> Jul 14 01:11:41 server01 kernel: [ 595.394231] [<ffffffff81050254>] ? thread_group_times+0x44/0xb0
> Jul 14 01:11:41 server01 kernel: [ 595.394392] [<ffffffff81059d41>] do_group_exit+0x51/0xc0
> Jul 14 01:11:41 server01 kernel: [ 595.394551] [<ffffffff81059dc7>] sys_exit_group+0x17/0x20
> Jul 14 01:11:41 server01 kernel: [ 595.394714] [<ffffffff815caea6>] system_call_fastpath+0x18/0x1d
> Jul 14 01:11:41 server01 kernel: [ 595.394921] ---[ end trace 738570e688acf099 ]---
>
> OK, so you had an OOM which has been handled by in-kernel oom handler
> (it killed 12021) and 12037 was in the same group. The warning tells us
> that it went through mem_cgroup_oom as well (otherwise it wouldn't have
> memcg_oom.wait_on_memcg set and the warning wouldn't trigger) and then
> it exited on the userspace request (by exit syscall).
>
> I do not see any way how, this could happen though. If mem_cgroup_oom
> is called then we always return CHARGE_NOMEM which turns into ENOMEM
> returned by __mem_cgroup_try_charge (invoke_oom must have been set to
> true). So if nobody screwed the return value on the way up to page
> fault handler then there is no way to escape.
>
> I will check the code.

OK, I guess I found it:
__do_fault
fault = filemap_fault
do_async_mmap_readahead
page_cache_async_readahead
ondemand_readahead
__do_page_cache_readahead
read_pages
readpages = ext3_readpages
mpage_readpages # Doesn't propagate ENOMEM
add_to_page_cache_lru
add_to_page_cache
add_to_page_cache_locked
mem_cgroup_cache_charge

So the read ahead most probably. Again! Duhhh. I will try to think
about a fix for this. One obvious place is mpage_readpages but
__do_page_cache_readahead ignores read_pages return value as well and
page_cache_async_readahead, even worse, is just void and exported as
such.

So this smells like a hard to fix bugger. One possible, and really ugly
way would be calling mem_cgroup_oom_synchronize even if handle_mm_fault
doesn't return VM_FAULT_ERROR, but that is a crude hack.
--
Michal Hocko
SUSE Labs
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Next message: Ole Tange: "mpt2sas/sd_mod: Adding back a removed disk handle"
Previous message: Randy Dunlap: "[PATCH] x86: fix ce4100.c build errors on i386"
In reply to: Michal Hocko: "Re: [PATCH for 3.2] memcg: do not trap chargers with full callstackon OOM"
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