Re: [PATCH] mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all()

From: David Hildenbrand <david@redhat.com>
To: "HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
	"Andrew Morton" <akpm@linux-foundation.org>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>,
	"linux-mm@kvack.org" <linux-mm@kvack.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>
Subject: Re: [PATCH] mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all()
Date: Thu, 8 Sep 2022 08:14:57 +0200	[thread overview]
Message-ID: <cef37de4-ac2c-9432-77d4-e5d2cad22bae@redhat.com> (raw)
In-Reply-To: <20220908024728.GB1491221@hori.linux.bs1.fc.nec.co.jp>

On 08.09.22 04:47, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Sep 07, 2022 at 01:57:45PM -0700, Andrew Morton wrote:
>> On Wed, 7 Sep 2022 21:11:57 +0900 Naoya Horiguchi <naoya.horiguchi@linux.dev> wrote:
>>
>>>
>>> NULL pointer dereference is triggered when calling thp split via debugfs
>>> on the system with offlined memory blocks.  With debug option enabled,
>>> the following kernel messages are printed out:
>>>
>>>    page:00000000467f4890 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x121c000
>>>    flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
>>>    raw: 0017fffc00000000 0000000000000000 dead000000000122 0000000000000000
>>>    raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
>>>    page dumped because: unmovable page
>>>    page:000000007d7ab72e is uninitialized and poisoned
>>>    page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>>>    ------------[ cut here ]------------
>>>    kernel BUG at include/linux/mm.h:1248!
>>>    invalid opcode: 0000 [#1] PREEMPT SMP PTI
>>>    CPU: 16 PID: 20964 Comm: bash Tainted: G          I        6.0.0-rc3-foll-numa+ #41
>>>    ...
>>>    RIP: 0010:split_huge_pages_write+0xcf4/0xe30
>>>
>>> This shows that page_to_nid() in page_zone() is unexpectedly called for an
>>> offlined memmap.
>>>
>>> Use pfn_to_online_page() to get struct page in PFN walker.
>>>
>>> Fixes: 49071d436b51 ("thp: add debugfs handle to split all huge pages")
>>
>> January of 2016!  Or was this a long-term bug which was recently
>> exposed by some other change?
> 
> Maybe yes, I confirmed that this issue reproduces in kernel 5.10 (released
> on Dec 13, 2020, which might not be so "recent"), but does not reproduce in
> kernel 5.4.  So I think that marking "5.10+" for stable is fine.

I fixed plenty of such issues in the past. For example:

aad5f69bc161 ("fs/proc/page.c: don't access uninitialized memmaps in fs/proc/page.c")

This one just wasn't found so far because it's triggered via
a debug interface.

The correct fixes tag would be:

Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")      [visible after d0dc12e86b319]

Exposed "recently" -- 2018 ;)

-- 
Thanks,

David / dhildenb