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Subject: Re: [syzbot] [mm?] kernel BUG in const_folio_flags
From: Muchun Song <muchun.song@linux.dev>
In-Reply-To: <ZfwJ0JOgcMCTcSgZ@localhost.localdomain>
Date: Fri, 22 Mar 2024 11:24:10 +0800
Cc: syzbot <syzbot+3b9148f91b7869120e81@syzkaller.appspotmail.com>,
 David Hildenbrand <david@redhat.com>,
 Matthew Wilcox <willy@infradead.org>,
 Andrew Morton <akpm@linux-foundation.org>,
 LKML <linux-kernel@vger.kernel.org>,
 Linux-MM <linux-mm@kvack.org>,
 syzkaller-bugs@googlegroups.com
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References: <0000000000006cfe98061423cde7@google.com>
 <812E97E8-668F-414D-9480-1D284834A034@linux.dev>
 <ZfwJ0JOgcMCTcSgZ@localhost.localdomain>
To: Oscar Salvador <osalvador@suse.de>


> On Mar 21, 2024, at 18:20, Oscar Salvador <osalvador@suse.de> wrote:
>=20
> On Thu, Mar 21, 2024 at 05:49:49PM +0800, Muchun Song wrote:
>> There are some more page dumping information from console:
>>=20
>> [ 61.367144][ T42] page: refcount:0 mapcount:0 =
mapping:0000000000000000 index:0xffff888028132880 pfn:0x28130
>> [ 61.371430][ T42] flags: =
0xfff80000000000(node=3D0|zone=3D1|lastcpupid=3D0xfff)
>> [ 61.374455][ T42] page_type: 0xffffffff()
>> [ 61.376096][ T42] raw: 00fff80000000000 ffff888015ecd540 =
dead000000000100 0000000000000000
>> [ 61.379994][ T42] raw: ffff888028132880 0000000000190000 =
00000000ffffffff 0000000000000000
>>=20
>> Alright, the page is freed (with a refcount of 0).
>=20
> Yes, basically the page changed betwen folio_test_large() (returned =
true
> for PG_Head) and the call to const_folio_flags() (which now returned
> false for PG_Head).
>=20
> As David pointed out, Willy is working on making PageHutelb more
> robust [1].
>=20
>=20
> [1] =
https://lore.kernel.org/linux-mm/20240314012506.1600378-1-willy@infradead.=
org/

Sorry, I am not on the CC list, so I didn't know this. But thank
you and David for this information, I think it could fix this problem.

Muchun,
Thanks.