netdev - Re: [PATCH net-next v5 1/7] vxlan: Restructure vxlan socket apis.

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Message-ID: <20130731164521.09c43fb8@nehalam.linuxnetplumber.net>
Date:	Wed, 31 Jul 2013 16:45:21 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Pravin B Shelar <pshelar@...ira.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 1/7] vxlan: Restructure vxlan socket apis.

On Wed, 31 Jul 2013 16:14:23 -0700
Pravin B Shelar <pshelar@...ira.com> wrote:

>  	/* Disable multicast loopback */
>  	inet_sk(sk)->mc_loop = 0;
> +	spin_lock(&vn->sock_lock);
> +	hlist_add_head_rcu(&vs->hlist, vs_head(net, port));
> +	spin_unlock(&vn->sock_lock);
>  

This change could potentially put two of the sockets with the
same port in the list.

There is an existing check in vxlan_sock_work to handle this
now. It does:
  create new socket (no locks)

  spin_lock
  if (udp_socket with that port exists)
      drop new socket
  else
      add to list
  spin_unlock

Your code seems to immediately put it on the list which
will cause duplicates if race occurs.
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