linux-kernel - Re: [syzbot] possible deadlock in pipe

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Date:   Tue, 27 Jul 2021 17:37:36 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Amir Goldstein <amir73il@...il.com>,
        syzbot <syzbot+579885d1a9a833336209@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        syzkaller-bugs@...glegroups.com, viro <viro@...iv.linux.org.uk>
Subject: Re: [syzbot] possible deadlock in pipe_lock (5)

On Sun, Jul 25, 2021 at 3:31 AM Hillf Danton <hdanton@...a.com> wrote:
>
> On Sat, 24 Jul 2021 12:07:20 -0700
> >syzbot found the following issue on:
> >
> >HEAD commit:    8cae8cd89f05 seq_file: disallow extremely large seq buffer..
> >git tree:       upstream
> >console output: https://syzkaller.appspot.com/x/log.txt?x=1083e8cc300000
> >kernel config:  https://syzkaller.appspot.com/x/.config?x=7273c75708b55890
> >dashboard link: https://syzkaller.appspot.com/bug?extid=579885d1a9a833336209
> >syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=163905f2300000
> >C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=165bd0ea300000
> >
> >The issue was bisected to:
> >
> >commit 82a763e61e2b601309d696d4fa514c77d64ee1be
> >Author: Miklos Szeredi <mszeredi@...hat.com>
> >Date:   Mon Dec 14 14:26:14 2020 +0000
> >
> >    ovl: simplify file splice
>
>
> If this commit is innocent then is it false positive lockdep warning again,
> given another report [1]?

Appears to be legit.

Attached partial revert + sync with ovl_write_iter() should fix it
(fingers crossed).

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

Thanks,
Miklos

View attachment "ovl-fix-deadlock-in-splice-write.patch" of type "text/x-patch" (1861 bytes)