linux-kernel - Re: [PATCH 1/1] af_packet: Raw socket destruction warning fix

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Date:	Wed, 10 Feb 2016 07:09:43 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Maninder Singh <maninder1.s@...sung.com>
Cc:	davem@...emloft.net, willemb@...gle.com, daniel@...earbox.net,
	edumazet@...gle.com, al.drozdov@...il.com, eyal.birger@...il.com,
	tklauser@...tanz.ch, fruggeri@...stanetworks.com,
	dwmw2@...radead.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, ajeet.y@...sung.com,
	pankaj.m@...sung.com, gh007.kim@...sung.com,
	hakbong5.lee@...sung.com, akhilesh.k@...sung.com,
	Vaneet Narang <v.narang@...sung.com>,
	Amit Nagal <amit.nagal@...sung.com>
Subject: Re: [PATCH 1/1] af_packet: Raw socket destruction warning fix

On Wed, 2016-02-10 at 17:35 +0530, Maninder Singh wrote:
> This Patch fixes below warning:-
> WARNING: at net/packet/af_packet.c:xxx packet_sock_destruct
> 
> There is following race between packet_rcv and packet_close
> which keeps unfree packet in receive queue.
> 
> CPU 1					CPU2
> packet_rcv
> 
> 					packet_close                       
> skb_set_owner_r(skb, sk);
> 
> 					skb_queue_purge(&sk->sk_receive_queue);
> 
> spin_lock(&sk->sk_receive_queue.lock);
> __skb_queue_tail(&sk->sk_receive_queue, skb);
> spin_unlock(&sk->sk_receive_queue.lock);

This absolutely can not happen.

CPU 1 holds rcu read lock, so cpu 2 can not possibly call
skb_queue_purge()

(cpu 1 is blocked in synchronize_net(), waiting that all cpus are no
longer in packet_rcv())

This patch does not address the root cause of your problem, and only
slightly changes probability for the bug to trigger.