Re: [BUG report] kernel NULL pointer dereference in split_huge_page with offlined memory block

From: David Hildenbrand <david@redhat.com>
To: Naoya Horiguchi <naoya.horiguchi@linux.dev>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Muchun Song <songmuchun@bytedance.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@suse.com>, Yang Shi <shy828301@gmail.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: Re: [BUG report] kernel NULL pointer dereference in split_huge_page with offlined memory block
Date: Wed, 7 Sep 2022 12:23:39 +0200	[thread overview]
Message-ID: <1481ce19-0a64-d1dc-4d89-4db71d6f7eb3@redhat.com> (raw)
In-Reply-To: <20220907100855.GA2894785@ik1-406-35019.vs.sakura.ne.jp>

On 07.09.22 12:08, Naoya Horiguchi wrote:
> Hi MM folks,

Hi,

> 
> When I'm testing memory hotremove with various settings, I found the following
> NULL-pointer dereference.  It reproduces easily with the folloing steps:
> 
>    $ echo offline > /sys/devices/system/memory/memoryN/state
>    $ echo 1 > /sys/kernel/debug/split_huge_pages
> 

That's weird, I don't immediately see how both features are related here, especially because it seems to fail quite early in split_huge_pages_write().

I was able to trigger it here as well, though, and I get on my kernel with debug options enabled:

[526045.808737] page:00000000467f4890 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x121c000
[526045.818306] flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
[526045.824842] raw: 0017fffc00000000 0000000000000000 dead000000000122 0000000000000000
[526045.832676] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[526045.840498] page dumped because: unmovable page
[526056.362715] page:000000007d7ab72e is uninitialized and poisoned
[526056.362720] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
[526056.374837] ------------[ cut here ]------------
[526056.379544] kernel BUG at include/linux/mm.h:1248!
[526056.384429] invalid opcode: 0000 [#1] PREEMPT SMP PTI
[526056.389570] CPU: 16 PID: 20964 Comm: bash Tainted: G          I        6.0.0-rc3-foll-numa+ #41
[526056.398347] Hardware name: Dell Inc. PowerEdge R740/0923K0, BIOS 2.11.2 004/21/2021
[526056.406087] RIP: 0010:split_huge_pages_write+0xcf4/0xe30
[526056.411495] Code: f9 ff ff 48 c7 c6 88 8e 4e a7 48 c7 c7 f8 0b a8 a7 e8 20 1c 3d 00 e9 54 f6 ff ff 48 c7 c6 38 06 4c a7 4c 89 e7 e8 5c 4a f7 ff <0f> 0b 48 8b 7c 24 08 be 02 00 00 00 e8 bb 6c 36 00 e9 11 f5 ff ff
[526056.430325] RSP: 0018:ffffae50e757fb40 EFLAGS: 00010292
[526056.435639] RAX: 0000000000000034 RBX: 0000000002d00000 RCX: 0000000000000000
[526056.442858] RDX: 0000000000000001 RSI: ffffffffa751a839 RDI: 00000000ffffffff
[526056.450077] RBP: 0000000000013937 R08: 0000000000000000 R09: ffffae50e757fa08
[526056.457296] R10: 0000000000000003 R11: ffffffffa793c768 R12: fffff00eb4000000
[526056.464514] R13: ffffae50e757fb7a R14: 000fffffffffffff R15: fffff00eb4000000
[526056.471733] FS:  00007fe35addf740(0000) GS:ffff8b71dc000000(0000) knlGS:0000000000000000
[526056.479906] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[526056.485738] CR2: 000055e87e606358 CR3: 00000004f5b46004 CR4: 00000000007706e0
[526056.492957] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[526056.500176] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[526056.507396] PKRU: 55555554
[526056.510196] Call Trace:
[526056.512734]  <TASK>
[526056.514929]  ? simple_setattr+0x40/0x60
[526056.518859]  ? vfs_mkobj+0x1b0/0x1c0
[526056.522529]  ? path_openat+0xb2e/0x1360
[526056.526456]  ? do_filp_open+0xa1/0x130
[526056.530296]  full_proxy_write+0x50/0x80
[526056.534229]  vfs_write+0xd7/0x3e0
[526056.537635]  ? fpregs_assert_state_consistent+0x22/0x50
[526056.542955]  ? exit_to_user_mode_prepare+0x3c/0x1d0
[526056.547929]  ? syscall_exit_to_user_mode+0x17/0x40
[526056.552808]  ksys_write+0x53/0xd0
[526056.556215]  do_syscall_64+0x58/0x80
[526056.559879]  ? exit_to_user_mode_prepare+0x3c/0x1d0
[526056.564846]  ? syscall_exit_to_user_mode+0x17/0x40
[526056.569726]  ? do_syscall_64+0x67/0x80
[526056.573563]  ? do_syscall_64+0x67/0x80
[526056.577404]  ? do_syscall_64+0x67/0x80
[526056.581244]  ? syscall_exit_to_user_mode+0x17/0x40
[526056.586120]  ? do_syscall_64+0x67/0x80
[526056.589961]  ? do_syscall_64+0x67/0x80
[526056.593801]  ? do_syscall_64+0x67/0x80
[526056.597641]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[526056.602779] RIP: 0033:0x7fe35ab01c17
[526056.606446] Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
[526056.625277] RSP: 002b:00007ffc1863c8d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[526056.632929] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fe35ab01c17
[526056.640147] RDX: 0000000000000002 RSI: 000055e87e7009a0 RDI: 0000000000000001
[526056.647366] RBP: 000055e87e7009a0 R08: 0000000000000000 R09: 0000000000000073
[526056.654586] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
[526056.661805] R13: 00007fe35abf8780 R14: 0000000000000002 R15: 00007fe35abf39e0
[526056.669028]  </TASK>

Looks like there is a page_to_nid() done in an offline memmap, which is wrong.

Usually, this indicates that a pfn_to_online_page() is missing in a PFN walker.

-- 
Thanks,

David / dhildenb