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

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Message-ID: <ZYJrVtMcNnwpdhhr@casper.infradead.org>
Date: Wed, 20 Dec 2023 04:19:34 +0000
From: Matthew Wilcox <willy@...radead.org>
To: syzbot <syzbot+9c40fd6eff0f3277cc9e@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] kernel BUG in add_to_swap

On Tue, Dec 19, 2023 at 05:09:25AM -0800, syzbot wrote:
> raw: 05ffc00000480011 dead000000000100 dead000000000122 ffff0000d90d0aa1
> raw: 0000000000020ffd 0000000000000000 00000002ffffffff ffff00012a670000
> page dumped because: VM_BUG_ON_FOLIO(!folio_test_uptodate(folio))

The missing part of the dump:

 page:0000000058ec4ec0 refcount:2 mapcount:0 mapping:0000000000000000 index:0x20ffd pfn:0x16fc28
 memcg:ffff00012a670000
 anon flags: 0x5ffc00000480011(locked|dirty|swapbacked|hwpoison|node=0|zone=2|lastcpupid=0x7ff)
 page_type: 0xffffffff()
 raw: 05ffc00000480011 dead000000000100 dead000000000122 ffff0000d90d0aa1
 raw: 0000000000020ffd 0000000000000000 00000002ffffffff ffff00012a670000
 page dumped because: VM_BUG_ON_FOLIO(!folio_test_uptodate(folio))

I'm not sure how we get an anonymous dirty folio that's not uptodate.
It's order-0, so that doesn't implicate any of the recent positive-order
work.