netdev - Re: [PATCH] tcp: possible race between tcp_done() and tcp

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Message-ID: <1c8f00de-552b-fff7-f8a8-cb98545ffafa@jp.fujitsu.com>
Date:   Thu, 30 Mar 2017 12:48:34 +0900
From:   Seiichi Ikarashi <s.ikarashi@...fujitsu.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     <netdev@...r.kernel.org>
Subject: Re: [PATCH] tcp: possible race between tcp_done() and tcp_poll()

On 2017-03-30 12:18, Eric Dumazet wrote:
> On Thu, 2017-03-30 at 11:55 +0900, Seiichi Ikarashi wrote:
> 
>> I got a report that receiving a RST packet but poll() got only POLLERR, no POLLIN|POLLRDHUP .
>> It was an old x86_64 kernel which does not include sk_state_{load,store} functions.
>> I suspected some race might have occur above.
> 
> It looks that a one-liner patch would be enough in tcp_done()
> 
> No need adding extra barriers

I agree.
sk->sk_shutdown seems not affect the behavior of both tcp_clear_xmit_timers()
and reqsk_fastopen_remove().

> 
> Untested patch :

Sorry, I cannot test it because I do not have a replication environment.

> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 1e319a525d51b0b603a5ccc5143381c752b9f2c7..4107d3fc00a53f768cdb885971a1067c810f5c9f 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3285,12 +3285,12 @@ void tcp_done(struct sock *sk)
>  	if (sk->sk_state == TCP_SYN_SENT || sk->sk_state == TCP_SYN_RECV)
>  		TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
>  
> +	sk->sk_shutdown = SHUTDOWN_MASK;
>  	tcp_set_state(sk, TCP_CLOSE);
>  	tcp_clear_xmit_timers(sk);
>  	if (req)
>  		reqsk_fastopen_remove(sk, req, false);
>  
> -	sk->sk_shutdown = SHUTDOWN_MASK;
>  
>  	if (!sock_flag(sk, SOCK_DEAD))
>  		sk->sk_state_change(sk);
> 
> 
> 
>