Re: fs, net: deadlock between bind/splice on af_unix

[Cong Wang <xiyou.wangcong@xxxxxxxxx>]

On Tue, Jan 31, 2017 at 10:14 AM, Mateusz Guzik <mguzik@xxxxxxxxxx> 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);