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From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Sun, 5 Feb 2017 23:22:12 -0800
Message-ID: <CAM_iQpVG+ybcv1DAc01y3c=CRmUgMqocEnp-efhVM0c-t4hZ0w@mail.gmail.com>
Subject: Re: fs, net: deadlock between bind/splice on af_unix
To: Mateusz Guzik <mguzik@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>, Al Viro <viro@zeniv.linux.org.uk>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        Rainer Weikusat <rweikusat@mobileactivedefense.com>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        netdev <netdev@vger.kernel.org>, Eric Dumazet <edumazet@google.com>,
        syzkaller <syzkaller@googlegroups.com>
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On Tue, Jan 31, 2017 at 10:14 AM, Mateusz Guzik <mguzik@redhat.com> wrote:
> On Mon, Jan 30, 2017 at 10:44:03PM -0800, Cong Wang wrote:
>> Mind being more specific?
>
> Consider 2 threads which bind the same socket, but with different paths.
>
> Currently exactly one file will get created, the one used to bind.
>
> With your patch both threads can succeed creating their respective
> files, but only one will manage to bind. The other one must error out,
> but it already created a file it is unclear what to do with.

In this case, it simply puts the path back:

        err = -EINVAL;
        if (u->addr)
                goto out_up;
[...]

out_up:
        mutex_unlock(&u->bindlock);
out_put:
        if (err)
                path_put(&path);
out:
        return err;


Which is what unix_release_sock() does too:

        if (path.dentry)
                path_put(&path);