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Date:   Mon, 18 Feb 2019 10:03:10 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Rong Chen <rong.a.chen@...el.com>
Cc:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-kernel@...r.kernel.org, LKP <lkp@...org>
Subject: Re: [LKP] efad4e475c [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI

On Mon 18-02-19 16:47:26, Rong Chen wrote:
> 
> On 2/18/19 3:08 PM, Michal Hocko wrote:
> > On Mon 18-02-19 13:28:23, kernel test robot wrote:
[...]
> > > [   40.305212] PGD 0 P4D 0
> > > [   40.308255] Oops: 0000 [#1] PREEMPT SMP PTI
> > > [   40.313055] CPU: 1 PID: 239 Comm: udevd Not tainted 5.0.0-rc4-00149-gefad4e4 #1
> > > [   40.321348] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> > > [   40.330813] RIP: 0010:page_mapping+0x12/0x80
> > > [   40.335709] Code: 5d c3 48 89 df e8 0e ad 02 00 85 c0 75 da 89 e8 5b 5d c3 0f 1f 44 00 00 53 48 89 fb 48 8b 43 08 48 8d 50 ff a8 01 48 0f 45 da <48> 8b 53 08 48 8d 42 ff 83 e2 01 48 0f 44 c3 48 83 38 ff 74 2f 48
> > > [   40.356704] RSP: 0018:ffff88801fa87cd8 EFLAGS: 00010202
> > > [   40.362714] RAX: ffffffffffffffff RBX: fffffffffffffffe RCX: 000000000000000a
> > > [   40.370798] RDX: fffffffffffffffe RSI: ffffffff820b9a20 RDI: ffff88801e5c0000
> > > [   40.378830] RBP: 6db6db6db6db6db7 R08: ffff88801e8bb000 R09: 0000000001b64d13
> > > [   40.386902] R10: ffff88801fa87cf8 R11: 0000000000000001 R12: ffff88801e640000
> > > [   40.395033] R13: ffffffff820b9a20 R14: ffff88801f145258 R15: 0000000000000001
> > > [   40.403138] FS:  00007fb2079817c0(0000) GS:ffff88801dd00000(0000) knlGS:0000000000000000
> > > [   40.412243] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [   40.418846] CR2: 0000000000000006 CR3: 000000001fa82000 CR4: 00000000000006a0
> > > [   40.426951] Call Trace:
> > > [   40.429843]  __dump_page+0x14/0x2c0
> > > [   40.433947]  is_mem_section_removable+0x24c/0x2c0
> > This looks like we are stumbling over an unitialized struct page again.
> > Something this patch should prevent from. Could you try to apply [1]
> > which will make __dump_page more robust so that we do not blow up there
> > and give some more details in return.
> 
> 
> Hi Hocko,
> 
> I have applied [1] and attached the dmesg file.

Thanks so the log confirms that this is really an unitialized struct
page
[   12.228622] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
[   12.231474] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
[   12.232135] ------------[ cut here ]------------
[   12.232649] kernel BUG at include/linux/mm.h:1020!

So now, we have to find out what has been left behind. Please see my
other email. Also could you give me faddr2line of the
is_mem_section_removable offset please? I assume it is 
is_pageblock_removable_nolock:
	if (!node_online(page_to_nid(page)))
		return false;
-- 
Michal Hocko
SUSE Labs

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