linux-kernel - Re: [BUG linux-next] Kernel panic found with linux-next-20160414

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Date:	Wed, 20 Apr 2016 09:11:50 -0700
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, sfr@...b.auug.org.au,
	Vlastimil Babka <vbabka@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [BUG linux-next] Kernel panic found with linux-next-20160414

On 4/20/2016 1:01 AM, Hugh Dickins wrote:
> On Tue, 19 Apr 2016, Shi, Yang wrote:
>> Hi folks,
>>
>> When I ran ltp on linux-next-20160414 on my ARM64 machine, I got the below
>> kernel panic:
>>
>> Unable to handle kernel paging request at virtual address ffffffc007846000
>> pgd = ffffffc01e21d000
>> [ffffffc007846000] *pgd=0000000000000000, *pud=0000000000000000
>> Internal error: Oops: 96000047 [#11] PREEMPT SMP
>> Modules linked in: loop
>> CPU: 7 PID: 274 Comm: systemd-journal Tainted: G      D
>> 4.6.0-rc3-next-20160414-WR8.0.0.0_standard+ #9
>> Hardware name: Freescale Layerscape 2085a RDB Board (DT)
>> task: ffffffc01e3fcf80 ti: ffffffc01ea8c000 task.ti: ffffffc01ea8c000
>> PC is at copy_page+0x38/0x120
>> LR is at migrate_page_copy+0x604/0x1660
>> pc : [<ffffff9008ff2318>] lr : [<ffffff900867cdac>] pstate: 20000145
>> sp : ffffffc01ea8ecd0
>> x29: ffffffc01ea8ecd0 x28: 0000000000000000
>> x27: 1ffffff7b80240f8 x26: ffffffc018196f20
>> x25: ffffffbdc01e1180 x24: ffffffbdc01e1180
>> x23: 0000000000000000 x22: ffffffc01e3fcf80
>> x21: ffffffc00481f000 x20: ffffff900a31d000
>> x19: ffffffbdc01207c0 x18: 0000000000000f00
>> x17: 0000000000000000 x16: 0000000000000000
>> x15: 0000000000000000 x14: 0000000000000000
>> x13: 0000000000000000 x12: 0000000000000000
>> x11: 0000000000000000 x10: 0000000000000000
>> x9 : 0000000000000000 x8 : 0000000000000000
>> x7 : 0000000000000000 x6 : 0000000000000000
>> x5 : 0000000000000000 x4 : 0000000000000000
>> x3 : 0000000000000000 x2 : 0000000000000000
>> x1 : ffffffc00481f080 x0 : ffffffc007846000
>>
>> Call trace:
>> Exception stack(0xffffffc021fc2ed0 to 0xffffffc021fc2ff0)
>> 2ec0:                                   ffffffbdc00887c0 ffffff900a31d000
>> 2ee0: ffffffc021fc30f0 ffffff9008ff2318 0000000020000145 0000000000000025
>> 2f00: ffffffbdc025a280 ffffffc020adc4c0 0000000041b58ab3 ffffff900a085fd0
>> 2f20: ffffff9008200658 0000000000000000 0000000000000000 ffffffbdc00887c0
>> 2f40: ffffff900b0f1320 ffffffc021fc3078 0000000041b58ab3 ffffff900a0864f8
>> 2f60: ffffff9008210010 ffffffc021fb8960 ffffff900867bacc 1ffffff8043f712d
>> 2f80: ffffffc021fc2fb0 ffffff9008210564 ffffffc021fc3070 ffffffc021fb8940
>> 2fa0: 0000000008221f78 ffffff900862f9c8 ffffffc021fc2fe0 ffffff9008215dc8
>> 2fc0: 1ffffff8043f8602 ffffffc021fc0000 ffffffc00968a000 ffffffc00221f080
>> 2fe0: f9407e11d00001f0 d61f02209103e210
>> [<ffffff9008ff2318>] copy_page+0x38/0x120
>> [<ffffff900867de7c>] migrate_page+0x74/0x98
>> [<ffffff90089ba418>] nfs_migrate_page+0x58/0x80
>> [<ffffff900867dffc>] move_to_new_page+0x15c/0x4d8
>> [<ffffff900867eec8>] migrate_pages+0x7c8/0x11f0
>> [<ffffff90085f8724>] compact_zone+0xdfc/0x2570
>> [<ffffff90085f9f78>] compact_zone_order+0xe0/0x170
>> [<ffffff90085fb688>] try_to_compact_pages+0x2e8/0x8f8
>> [<ffffff90085913a0>] __alloc_pages_direct_compact+0x100/0x540
>> [<ffffff9008592420>] __alloc_pages_nodemask+0xc40/0x1c58
>> [<ffffff90086887e8>] khugepaged+0x468/0x19c8
>> [<ffffff9008301700>] kthread+0x248/0x2c0
>> [<ffffff9008206610>] ret_from_fork+0x10/0x40
>> Code: d281f012 91020021 f1020252 d503201f (a8000c02)
>>
>>
>> I did some initial investigation and found it is caused by DEBUG_PAGEALLOC
>> and CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT. And, mainline 4.6-rc3 works well.
>>
>> It should be not arch specific although I got it caught on ARM64. I suspect
>> this might be caused by Hugh's huge tmpfs patches.
>
> Thanks for testing.  It might be caused by my patches, but I don't think
> that's very likely.  This is page migraton for compaction, in the service
> of anon THP's khugepaged; and I wonder if you were even exercising huge
> tmpfs when running LTP here (it certainly can be done: I like to mount a
> huge tmpfs on /opt/ltp and install there, with shmem_huge 2 so any other
> tmpfs mounts are also huge).

Some further investigation shows I got the panic even though I don't 
have tmpfs mounted with huge=1 or set shmem_huge to 2.

>
> There are compaction changes in linux-next too, but I don't see any
> reason why they'd cause this.  I don't know arm64 traces enough to know
> whether it's the source page or the destination page for the copy, but
> it looks as if it has been freed (and DEBUG_PAGEALLOC unmapped) before
> reaching migration's copy.

The fault address is passed by x0, which is dest in the implementation 
of copy_page, so it is the destination page.

>
> Needs more debugging, I'm afraid: is it reproducible?

Yes, as long as I enable those two PAGEALLOC debug options, I can get 
the panic once I run ltp. But, it is not caused any specific ltp test 
case directly, the panic happens randomly during ltp is running.

Thanks,
Yang

>
> Hugh
>