linux-kernel - Re: [syzbot] [mm?] kernel BUG in const_folio

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Message-Id: <1349A15A-341F-4EE4-AD40-805A97A9FFD1@linux.dev>
Date: Fri, 22 Mar 2024 11:24:10 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Oscar Salvador <osalvador@...e.de>
Cc: syzbot <syzbot+3b9148f91b7869120e81@...kaller.appspotmail.com>,
 David Hildenbrand <david@...hat.com>,
 Matthew Wilcox <willy@...radead.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 LKML <linux-kernel@...r.kernel.org>,
 Linux-MM <linux-mm@...ck.org>,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] kernel BUG in const_folio_flags



> On Mar 21, 2024, at 18:20, Oscar Salvador <osalvador@...e.de> wrote:
> 
> On Thu, Mar 21, 2024 at 05:49:49PM +0800, Muchun Song wrote:
>> There are some more page dumping information from console:
>> 
>> [ 61.367144][ T42] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888028132880 pfn:0x28130
>> [ 61.371430][ T42] flags: 0xfff80000000000(node=0|zone=1|lastcpupid=0xfff)
>> [ 61.374455][ T42] page_type: 0xffffffff()
>> [ 61.376096][ T42] raw: 00fff80000000000 ffff888015ecd540 dead000000000100 0000000000000000
>> [ 61.379994][ T42] raw: ffff888028132880 0000000000190000 00000000ffffffff 0000000000000000
>> 
>> Alright, the page is freed (with a refcount of 0).
> 
> 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).
> 
> As David pointed out, Willy is working on making PageHutelb more
> robust [1].
> 
> 
> [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.