Re: [syzbot] WARNING in register_shrinker_prepared

[Andrew Morton]

(cc Roman)

On Mon, 06 Jun 2022 10:17:34 -0700 syzbot <syzbot+300d27c79fe6d4cbcc39@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    1cfd968b58a1 Add linux-next specific files for 20220603
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=12f7b6b3f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=7da8386e3742814f
> dashboard link: https://syzkaller.appspot.com/bug?extid=300d27c79fe6d4cbcc39
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=103e5177f00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13545057f00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+300d27c79fe6d4cbcc39@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> loop0: detected capacity change from 0 to 20
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 3694 at mm/vmscan.c:681 register_shrinker_prepared+0x119/0x150 mm/vmscan.c:681

That's

	WARN_ON_ONCE(shrinker_debugfs_add(shrinker));

I assume that debugfs_create_dir() failed.  Please see the NOTE: in
that function's kerneldoc.