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Subject: Re: [Bug 202149] New: NULL Pointer Dereference in __split_huge_pmd on
 PPC64LE
From: Matt Corallo <kernel@bluematt.me>
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Date: Wed, 9 Jan 2019 08:38:28 -0500
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References: <bug-202149-27@https.bugzilla.kernel.org/>
 <20190104170459.c8c7fa57ba9bc8a69dee5666@linux-foundation.org>
 <87ef9nk4cj.fsf@linux.ibm.com>
 <ed4bea40-cf9e-89a1-f99a-3dbd6249847f@bluematt.me>
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To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
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Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
 bugzilla-daemon@bugzilla.kernel.org, linuxppc-dev@lists.ozlabs.org
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

It's normal daily usage on a workstation (TALOS 2). I've seen it at least tw=
ice, both times in rustc, though I've run rustc more times than I can count.=
 Note that the program that triggered it was running in lxc and it only happ=
ened after upgrading to 4.19.

> On Jan 9, 2019, at 06:50, Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> wr=
ote:
>=20
> Matt Corallo <kernel@bluematt.me> writes:
>=20
>> .config follows. I have not tested with 64K pages as, sadly, I have a=20
>> large BTRFS volume that was formatted on x86, and am thus stuck with 4K=20=

>> pages. Note that this is roughly the Debian kernel, so it has whatever=20=

>> patches Debian defaults to applying, a list of which follows.
>>=20
>=20
> What is the test you are running? I tried a 4K page size config on P9. I
> am running ltp test suite there. Also tried few thp memremap tests.
> Nothing hit that.
>=20
> root@:~/tests/ltp/testcases/kernel/mem/thp# getconf  PAGESIZE
> 4096
> root@ltc-boston123:~/tests/ltp/testcases/kernel/mem/thp# grep thp /proc/vm=
stat=20
> thp_fault_alloc 641141
> thp_fault_fallback 0
> thp_collapse_alloc 90
> thp_collapse_alloc_failed 0
> thp_file_alloc 0
> thp_file_mapped 0
> thp_split_page 1
> thp_split_page_failed 0
> thp_deferred_split_page 641150
> thp_split_pmd 24
> thp_zero_page_alloc 1
> thp_zero_page_alloc_failed 0
> thp_swpout 0
> thp_swpout_fallback 0
> root@:~/tests/ltp/testcases/kernel/mem/thp#=20
>=20
> -aneesh
>=20