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Date: Fri, 19 Jul 2013 10:23:39 +0200 From: "azurIt" <azurit@...ox.sk> To: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...e.cz> Cc: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, cgroups mailinglist <cgroups@...r.kernel.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, <righi.andrea@...il.com> Subject: Re: [PATCH for 3.2] memcg: do not trap chargers with full callstack on OOM > CC: linux-kernel@...r.kernel.org, linux-mm@...ck.org, "cgroups mailinglist" <cgroups@...r.kernel.org>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, righi.andrea@...il.com >On Tue, Jul 16, 2013 at 12:48:30PM -0400, Johannes Weiner wrote: >> On Tue, Jul 16, 2013 at 06:09:05PM +0200, Michal Hocko wrote: >> > On Tue 16-07-13 11:35:44, Johannes Weiner wrote: >> > > On Mon, Jul 15, 2013 at 06:00:06PM +0200, Michal Hocko wrote: >> > > > 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@...xchg.org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, "cgroups mailinglist" <cgroups@...r.kernel.org>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, righi.andrea@...il.com >> > > > > > >> CC: "Johannes Weiner" <hannes@...xchg.org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, "cgroups mailinglist" <cgroups@...r.kernel.org>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, righi.andrea@...il.com >> > > > > > >>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. > >I fixed it by disabling the OOM killer altogether for readahead code. >We don't do it globally, we should not do it in the memcg, these are >optional allocations/charges. > >I also disabled it for kernel faults triggered from within a syscall >(copy_*user, get_user_pages), which should just return -ENOMEM as >usual (unless it's nested inside a userspace fault). The only >downside is that we can't get around annotating userspace faults >anymore, so every architecture fault handler now passes >FAULT_FLAG_USER to handle_mm_fault(). Makes the series a little less >self-contained, but it's not unreasonable. > >It's easy to detect leaks now by checking if the memcg OOM context is >setup and we are not returning VM_FAULT_OOM. > >Here is a combined diff based on 3.2. azurIt, any chance you could >give this a shot? I tested it on my local machines, but you have a >known reproducer of fairly unlikely scenarios... I will be out of office between 25.7. and 1.8. and I don't want to run anything which can potentially do an outage of our services. I will test this patch after 2.8. Should I use also previous patches of this one is enough? Thank you very much Johannes. azur -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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