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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Tue, 3 Mar 2020 09:34:42 +0200
Message-ID: <CAOQ4uxirc1WwQOzE4Qq=k2R0ntGNTGYsot1b63DPkwCbUYjyZA@mail.gmail.com>
Subject: Re: WARNING: bad unlock balance in ovl_llseek
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     syzbot <syzbot+66a9752fa927f745385e@syzkaller.appspotmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Mon, Mar 2, 2020 at 2:19 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Mar 2, 2020 at 1:17 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Mon, Mar 2, 2020 at 12:10 PM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > > > =====================================
> > > > WARNING: bad unlock balance detected!
> > > > 5.6.0-rc3-syzkaller #0 Not tainted
> > > > -------------------------------------
> > > > syz-executor194/8947 is trying to release lock (&ovl_i_lock_key[depth]) at:
> > > > [<ffffffff828b7835>] ovl_inode_unlock fs/overlayfs/overlayfs.h:328 [inline]
> > > > [<ffffffff828b7835>] ovl_llseek+0x215/0x2c0 fs/overlayfs/file.c:193
> > > > but there are no more locks to release!
> > > >
> > >
> > > This is strange. I don't see how that can happen nor how my change would
> > > have caused this regression. If anything, the lock chance may have brought
> > > a bug in stack file ops to light, but don't see the bug.
> >
> > The bug is that ovl_inode_lock() is interruptible and that the caller
> > doesn't check for error.
> >
> > I think the fix is to make this lock uninterruptible (probably rename
> > the current helper to _interruptible and use the current name as the
> > uninterruptible version).
> >
>

Miklos,

Added the patch to ovl-fixes along with another ovl fix for fast track 5.6.

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

Thanks,
Amir.