linux-kernel - Re: possible deadlock in ovl_copy_up

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Message-ID: <CAJfpegsDfJMsT8OJVYuUFpNz94ex0fm5Z-e2Gp=cUgXsb_L-Jg@mail.gmail.com>
Date:   Thu, 18 Oct 2018 10:41:17 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     syzbot+3ef5c0d1a5cb0b21e6be@...kaller.appspotmail.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: possible deadlock in ovl_copy_up_start

On Thu, Oct 18, 2018 at 8:26 AM, Amir Goldstein <amir73il@...il.com> wrote:

> Can someone tell me what the expected behavior of a nested
> mutex_lock_interruptible(&lock); ?
>
> Why does the reproducer only warn and not really deadlock.
> It is because that is considered the lesser evil?
> and obviously, then inner unlock releases the outer lock?

No, it's not the same lock, just the same lock class (first one is
OVL_I(d_inode(old))->lock, the other is
OVL_I(d_inode(new->d_parent)))->lock).

So we could possibly get away with annotating with
mutex_lock_nested().  Is this the only place that ovl_i_lock is
nested?

Thanks,
Miklos