netdev - Re: Crash when receiving FIN-ACK in TCP_FIN

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Date:   Wed, 30 Oct 2019 17:38:28 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Neal Cardwell <ncardwell@...gle.com>
Cc:     Netdev <netdev@...r.kernel.org>, Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: Crash when receiving FIN-ACK in TCP_FIN_WAIT1 state



On 10/30/19 11:27 AM, Subash Abhinov Kasiviswanathan wrote:
>> Thanks. Do you mind sharing what your patch looked like, so we can
>> understand precisely what was changed?
>>
>> Also, are you able to share what the workload looked like that tickled
>> this issue? (web client? file server?...)
> 
> Sure. This was seen only on our regression racks and the workload there
> is a combination of FTP, browsing and other apps.
> 
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 4374196..9af7497 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -232,7 +232,8 @@ struct tcp_sock {
>                 fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
>                 fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */
>                 is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
> -               unused:2;
> +               unused:1,
> +               wqp_called:1;
>         u8      nonagle     : 4,/* Disable Nagle algorithm?             */
>                 thin_lto    : 1,/* Use linear timeouts for thin streams */
>                 recvmsg_inq : 1,/* Indicate # of bytes in queue upon recvmsg */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 1a1fcb3..0c29bdd 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2534,6 +2534,9 @@ void tcp_write_queue_purge(struct sock *sk)
>         INIT_LIST_HEAD(&tcp_sk(sk)->tsorted_sent_queue);
>         sk_mem_reclaim(sk);
>         tcp_clear_all_retrans_hints(tcp_sk(sk));
> +       tcp_sk(sk)->highest_sack = NULL;
> +       tcp_sk(sk)->sacked_out = 0;
> +       tcp_sk(sk)->wqp_called = 1;

What is this wqp_called exactly ?