linux-kernel - Re: [syzbot] [netfs?] kernel BUG in folio

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Message-ID: <Z7dVOaTWTVCojNzr@casper.infradead.org>
Date: Thu, 20 Feb 2025 16:15:53 +0000
From: Matthew Wilcox <willy@...radead.org>
To: syzbot <syzbot+c0dc46208750f063d0e0@...kaller.appspotmail.com>
Cc: Dominique Martinet <asmadeus@...ewreck.org>, v9fs@...ts.linux.dev,
	dhowells@...hat.com, jlayton@...nel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	netfs@...ts.linux.dev, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

On Thu, Feb 20, 2025 at 08:00:24AM -0800, syzbot wrote:
> ------------[ cut here ]------------
> kernel BUG at mm/filemap.c:1499!

Tried to unlock a folio that wasn't locked.

The entire log is interesting:

https://syzkaller.appspot.com/x/log.txt?x=12af2fdf980000

It injects a failure which hits p9_tag_alloc() (so adding the 9p people
to the cc)

The page dump is:

 page: refcount:1 mapcount:0 mapping:ffff888035b30890 index:0x0 pfn:0x37e9a
 memcg:ffff88801c6be000
 aops:v9fs_addr_operations ino:2721d72 dentry name(?):"file0"
 flags: 0xfff20000000020(lru|node=0|zone=1|lastcpupid=0x7ff)
 raw: 00fff20000000020 ffffea0000e1d1c8 ffff88801b0b31a0 ffff888035b30890
 raw: 0000000000000000 0000000000000000 00000001ffffffff ffff88801c6be000
 page dumped because: VM_BUG_ON_FOLIO(!folio_test_locked(folio))

> Call Trace:
>  <TASK>
>  netfs_perform_write+0xc04/0x2140 fs/netfs/buffered_write.c:400
>  netfs_buffered_write_iter_locked fs/netfs/buffered_write.c:445 [inline]
>  netfs_file_write_iter+0x494/0x550 fs/netfs/buffered_write.c:484
>  v9fs_file_write_iter+0x9b/0x100 fs/9p/vfs_file.c:407
>  new_sync_write fs/read_write.c:586 [inline]
>  vfs_write+0x5ae/0x1150 fs/read_write.c:679
>  ksys_write+0x12b/0x250 fs/read_write.c:731