Re: [patch 0/7] improve memcg oom killer robustness v2

[Johannes Weiner]

On Tue, Sep 10, 2013 at 08:13:59PM +0200, azurIt wrote:
> >On Mon, Sep 09, 2013 at 09:59:17PM +0200, azurIt wrote:
> >> >On Mon, Sep 09, 2013 at 03:10:10PM +0200, azurIt wrote:
> >> >> >Hi azur,
> >> >> >
> >> >> >On Wed, Sep 04, 2013 at 10:18:52AM +0200, azurIt wrote:
> >> >> >> > CC: "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx>, "Michal Hocko" <mhocko@xxxxxxx>, "David Rientjes" <rientjes@xxxxxxxxxx>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx>, "KOSAKI Motohiro" <kosaki.motohiro@xxxxxxxxxxxxxx>, linux-mm@xxxxxxxxx, cgroups@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> >> >> >> >Hello azur,
> >> >> >> >
> >> >> >> >On Mon, Sep 02, 2013 at 12:38:02PM +0200, azurIt wrote:
> >> >> >> >> >>Hi azur,
> >> >> >> >> >>
> >> >> >> >> >>here is the x86-only rollup of the series for 3.2.
> >> >> >> >> >>
> >> >> >> >> >>Thanks!
> >> >> >> >> >>Johannes
> >> >> >> >> >>---
> >> >> >> >> >
> >> >> >> >> >
> >> >> >> >> >Johannes,
> >> >> >> >> >
> >> >> >> >> >unfortunately, one problem arises: I have (again) cgroup which cannot be deleted :( it's a user who had very high memory usage and was reaching his limit very often. Do you need any info which i can gather now?
> >> >> >> >
> >> >> >> >Did the OOM killer go off in this group?
> >> >> >> >
> >> >> >> >Was there a warning in the syslog ("Fixing unhandled memcg OOM
> >> >> >> >context")?
> >> >> >> 
> >> >> >> 
> >> >> >> 
> >> >> >> Ok, i see this message several times in my syslog logs, one of them is also for this unremovable cgroup (but maybe all of them cannot be removed, should i try?). Example of the log is here (don't know where exactly it starts and ends so here is the full kernel log):
> >> >> >> http://watchdog.sk/lkml/oom_syslog.gz
> >> >> >There is an unfinished OOM invocation here:
> >> >> >
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715112] Fixing unhandled memcg OOM context set up from:
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715191]  [<ffffffff811105c2>] T.1154+0x622/0x8f0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715274]  [<ffffffff8111153e>] mem_cgroup_cache_charge+0xbe/0xe0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715357]  [<ffffffff810cf31c>] add_to_page_cache_locked+0x4c/0x140
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715443]  [<ffffffff810cf432>] add_to_page_cache_lru+0x22/0x50
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715526]  [<ffffffff810cfdd3>] find_or_create_page+0x73/0xb0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715608]  [<ffffffff811493ba>] __getblk+0xea/0x2c0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715692]  [<ffffffff8114ca73>] __bread+0x13/0xc0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715774]  [<ffffffff81196968>] ext3_get_branch+0x98/0x140
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715859]  [<ffffffff81197557>] ext3_get_blocks_handle+0xd7/0xdc0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715942]  [<ffffffff81198304>] ext3_get_block+0xc4/0x120
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716023]  [<ffffffff81155c3a>] do_mpage_readpage+0x38a/0x690
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716107]  [<ffffffff81155f8f>] mpage_readpage+0x4f/0x70
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716188]  [<ffffffff811973a8>] ext3_readpage+0x28/0x60
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716268]  [<ffffffff810cfa48>] filemap_fault+0x308/0x560
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716350]  [<ffffffff810ef898>] __do_fault+0x78/0x5a0
> >> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716433]  [<ffffffff810f2ab4>] handle_pte_fault+0x84/0x940
> >> >> >
> >> >> >__getblk() has this weird loop where it tries to instantiate the page,
> >> >> >frees memory on failure, then retries.  If the memcg goes OOM, the OOM
> >> >> >path might be entered multiple times and each time leak the memcg
> >> >> >reference of the respective previous OOM invocation.
> >> >> >
> >> >> >There are a few more find_or_create() sites that do not propagate an
> >> >> >error and it's incredibly hard to find out whether they are even taken
> >> >> >during a page fault.  It's not practical to annotate them all with
> >> >> >memcg OOM toggles, so let's just catch all OOM contexts at the end of
> >> >> >handle_mm_fault() and clear them if !VM_FAULT_OOM instead of treating
> >> >> >this like an error.
> >> >> >
> >> >> >azur, here is a patch on top of your modified 3.2.  Note that Michal
> >> >> >might be onto something and we are looking at multiple issues here,
> >> >> >but the log excert above suggests this fix is required either way.
> >> >> 
> >> >> 
> >> >> 
> >> >> 
> >> >> Johannes, is this still up to date? Thank you.
> >> >
> >> >No, please use the following on top of 3.2 (i.e. full replacement, not
> >> >incremental to what you have):
> >> 
> >> 
> >> 
> >> Unfortunately it didn't compile:
> >> 
> >> 
> >> 
> >> 
> >>   LD      vmlinux.o
> >>   MODPOST vmlinux.o
> >> WARNING: modpost: Found 4924 section mismatch(es).
> >> To see full details build your kernel with:
> >> 'make CONFIG_DEBUG_SECTION_MISMATCH=y'
> >>   GEN     .version
> >>   CHK     include/generated/compile.h
> >>   UPD     include/generated/compile.h
> >>   CC      init/version.o
> >>   LD      init/built-in.o
> >>   LD      .tmp_vmlinux1
> >> arch/x86/built-in.o: In function `do_page_fault':
> >> (.text+0x26a77): undefined reference to `handle_mm_fault'
> >> mm/built-in.o: In function `fixup_user_fault':
> >> (.text+0x224d3): undefined reference to `handle_mm_fault'
> >> mm/built-in.o: In function `__get_user_pages':
> >> (.text+0x24a0f): undefined reference to `handle_mm_fault'
> >> make: *** [.tmp_vmlinux1] Error 1
> >
> >Oops, sorry about that.  Must be configuration dependent because it
> >works for me (and handle_mm_fault is obviously defined).
> >
> >Do you have warnings earlier in the compilation?  You can use make -s
> >to filter out everything but warnings.
> >
> >Or send me your configuration so I can try to reproduce it here.
> >
> >Thanks!
> 
> 
> Johannes,
> 
> the server went down early in the morning, the symptoms were similar as before - huge I/O. Can't tell what exactly happened since I wasn't able to login even on the console. But I have some info:
>  - applications were able to write to HDD so it wasn't deadlocked as before
>  - here is how it looked on graphs: http://watchdog.sk/lkml/graphs.jpg
>  - server wasn't responding from 6:36, it was down between 6:54 and 7:02 (i had to hard reboot it), I was awoken at 6:36 by really creepy sound from my phone ;)
>  - my 'load check' script successfully killed apache at 6:41 but it didn't help as you can see
>  - i have one screen with info from atop from time 6:44, looks like i/o was done by init (??!): http://watchdog.sk/lkml/atop.jpg (ignore swap warning, i have no swap)
>  - also other type of logs are available
>  - nothing like this happened before

That IO from init looks really screwy, I have no idea what's going on
on that machine, but it looks like there is more than just a memcg
problem...  Any chance your thirdparty security patches are concealing
kernel daemon activity behind the init process and the IO is actually
coming from a kernel thread like the flushers or kswapd?

Are there OOM kill messages in the syslog?

> What do you think? I'm now running kernel with your previous patch, not with the newest one.

Which one exactly?  Can you attach the diff?
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