linux-kernel - Re: [syzbot] [overlayfs?] possible deadlock in seq_read

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Message-ID: <CAOQ4uxiUoWO10a7UH5UweQ_1f+Fu+jSKPO66yAv80izyx9hBGg@mail.gmail.com>
Date: Wed, 20 Dec 2023 05:53:38 +0200
From: Amir Goldstein <amir73il@...il.com>
To: syzbot <syzbot+da4f9f61f96525c62cc7@...kaller.appspotmail.com>
Cc: axboe@...nel.dk, hch@....de, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, rafael@...nel.org, syzkaller-bugs@...glegroups.com, 
	Christian Brauner <brauner@...nel.org>, David Howells <dhowells@...hat.com>
Subject: Re: [syzbot] [overlayfs?] possible deadlock in seq_read_iter (2)

On Wed, Dec 20, 2023 at 2:30 AM syzbot
<syzbot+da4f9f61f96525c62cc7@...kaller.appspotmail.com> wrote:
>
> syzbot has bisected this issue to:
>
> commit 1e8c813b083c4122dfeaa5c3b11028331026e85d
> Author: Christoph Hellwig <hch@....de>
> Date:   Wed May 31 12:55:32 2023 +0000
>
>     PM: hibernate: don't use early_lookup_bdev in resume_store
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14b15592e80000
> start commit:   2cf4f94d8e86 Merge tag 'scsi-fixes' of git://git.kernel.or..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=16b15592e80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=12b15592e80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e5751b3a2226135d
> dashboard link: https://syzkaller.appspot.com/bug?extid=da4f9f61f96525c62cc7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=176a4f49e80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=154aa8d6e80000
>
> Reported-by: syzbot+da4f9f61f96525c62cc7@...kaller.appspotmail.com
> Fixes: 1e8c813b083c ("PM: hibernate: don't use early_lookup_bdev in resume_store")
>

I'm not sure this bisection is reliable, so I wouldn't use this Fixes tag.
The reproducer may be a little flakey.

Anyway, this is just one of many problems, real or false positives,
related to the unholy dependency which sendfile() creates between
locks on two different filesystems.

I think those changes that are queued for 6.8 are going so fix this class
of problems:

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.rw

Thanks,
Amir.