Received-SPF: pass (google.com: domain of linux-kernel+bounces-133815-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Precedence: bulk
MIME-Version: 1.0
References: <CAOQ4uxhm5m9CvX0y2RcJGuP=vryZLp9M+tS6vH1o_9BGUqxrvg@mail.gmail.com>
 <00000000000039026a06155b3a12@google.com> <20240405162333.GU538574@ZenIV>
In-Reply-To: <20240405162333.GU538574@ZenIV>
From: Amir Goldstein <amir73il@gmail.com>
Date: Sat, 6 Apr 2024 08:34:02 +0300
Message-ID: <CAOQ4uxgJ5URyDG26Ny5Cmg7DceOeG-exNt9N346pq9U0TmcYtg@mail.gmail.com>
Subject: Re: [syzbot] [kernfs?] possible deadlock in kernfs_fop_llseek
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: syzbot <syzbot+9a5b0ced8b1bfb238b56@syzkaller.appspotmail.com>, 
	brauner@kernel.org, gregkh@linuxfoundation.org, hch@lst.de, jack@suse.cz, 
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, 
	miklos@szeredi.hu, syzkaller-bugs@googlegroups.com, tj@kernel.org, 
	valesini@yandex-team.ru
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Fri, Apr 5, 2024 at 7:23=E2=80=AFPM Al Viro <viro@zeniv.linux.org.uk> wr=
ote:
>
> On Fri, Apr 05, 2024 at 08:37:03AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot tried to test the proposed patch but the build/boot failed:
>
> WTF?  The patch is
>
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index e9df2f87072c6..8502ef68459b9 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -636,11 +636,18 @@ static int kernfs_fop_open(struct inode *inode, str=
uct file *file)
>          * each file a separate locking class.  Let's differentiate on
>          * whether the file has mmap or not for now.
>          *
> -        * Both paths of the branch look the same.  They're supposed to
> +        * For similar reasons, writable and readonly files are given dif=
ferent
> +        * lockdep key, because the writable file /sys/power/resume may c=
all vfs
> +        * lookup helpers for arbitrary paths and readonly files can be r=
ead by
> +        * overlayfs from vfs helpers when sysfs is a lower layer of over=
alyfs.
> +        *
> +        * All three cases look the same.  They're supposed to
>          * look that way and give @of->mutex different static lockdep key=
s.
>          */
>         if (has_mmap)
>                 mutex_init(&of->mutex);
> +       else if (file->f_mode & FMODE_WRITE)
> +               mutex_init(&of->mutex);
>         else
>                 mutex_init(&of->mutex);
>
> How could it possibly trigger boot failure?  Test the parent, perhaps?

Let's try again, rebased on current master:

#syz test: https://github.com/amir73il/linux/ vfs-fixes

Thanks,
Amir.