Re: [mm? 4.15-rc7] Random oopses under memory pressure.

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@suse.com
Cc: linux-mm@kvack.org
Subject: Re: [mm? 4.15-rc7] Random oopses under memory pressure.
Date: Wed, 10 Jan 2018 22:37:52 +0900	[thread overview]
Message-ID: <201801102237.BED34322.QOOJMFFFHVLSOt@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20180110124519.GU1732@dhcp22.suse.cz>

Michal Hocko wrote:
> On Wed 10-01-18 20:49:56, Tetsuo Handa wrote:
> > Tetsuo Handa wrote:
> > > I can hit this bug with Linux 4.11 and 4.8. (i.e. at least all 4.8+ have this bug.)
> > > So far I haven't hit this bug with Linux 4.8-rc3 and 4.7.
> > > Does anyone know what is happening?
> > 
> > I simplified the reproducer and succeeded to reproduce this bug with both
> > i7-2630QM (8 core) and i5-4440S (4 core). Thus, I think that this bug is
> > not architecture specific.
> 
> Can you see the same with 64b kernel?

No. I can hit this bug with only x86_32 kernels.
But if the cause is not specific to 32b, this might be silent memory corruption.

> It smells like a ref count imbalance and premature page free to me. Can
> you try to bisect this?

Too difficult to bisect, but at least I can hit this bug with 4.8+ kernels.

The XXX in "count:XXX mapcount:XXX mapping:XXX index:XXX" are rather random
as if they are overwritten.

[   44.103192] page:5a5a0697 count:-1055023618 mapcount:-1055030029 mapping:26f4be11 index:0xc11d7c83
[   44.103196] flags: 0xc10528fe(waiters|error|referenced|uptodate|dirty|lru|active|reserved|private_2|mappedtodisk|swapbacked)
[   44.103200] raw: c10528fe c114fff7 c11d7c83 c11d84f2 c11d9dfe c11daa34 c11daaa0 c13e65df
[   44.103201] raw: c13e4a1c c13e4c62
[   44.103202] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) <= 0)
[   44.103203] page->mem_cgroup:35401b27

[  192.152510] BUG: Bad page state in process a.out  pfn:18566
[  192.152513] page:f72997f0 count:0 mapcount:8 mapping:f118f5a4 index:0x0
[  192.152516] flags: 0x19010019(locked|uptodate|dirty|mappedtodisk)
[  192.152520] raw: 19010019 f118f5a4 00000000 00000007 00000000 f7299804 f7299804 00000000
[  192.152521] raw: 00000000 00000000
[  192.152521] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
[  192.152522] bad because of flags: 0x1(locked)

[   77.872133] BUG: Bad page state in process a.out  pfn:1873a
[   77.872136] page:f729e110 count:0 mapcount:6 mapping:f1187224 index:0x0
[   77.872138] flags: 0x19010019(locked|uptodate|dirty|mappedtodisk)
[   77.872141] raw: 19010019 f1187224 00000000 00000005 00000000 f729e124 f729e124 00000000
[   77.872141] raw: 00000000 00000000
[   77.872142] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
[   77.872142] bad because of flags: 0x1(locked)

[  188.992549] BUG: Bad page state in process a.out  pfn:197ea
[  188.992551] page:f72c7c90 count:0 mapcount:12 mapping:f11b8ca4 index:0x0
[  188.992554] flags: 0x19010019(locked|uptodate|dirty|mappedtodisk)
[  188.992557] raw: 19010019 f11b8ca4 00000000 0000000b 00000000 f72c7ca4 f72c7ca4 00000000
[  188.992557] raw: 00000000 00000000
[  188.992558] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
[  188.992559] bad because of flags: 0x1(locked)

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