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

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Message-ID: <ZfwJ0JOgcMCTcSgZ@localhost.localdomain>
Date: Thu, 21 Mar 2024 11:20:00 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Muchun Song <muchun.song@...ux.dev>
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 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/

-- 
Oscar Salvador
SUSE Labs