Subject: Re: Crash when receiving FIN-ACK in TCP_FIN_WAIT1 state

From: Subash Abhinov Kasiviswanathan <[email-masked]>
Date: Wed, 30 Oct 2019 12:27:37 -0600

> 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;
         tcp_sk(sk)->packets_out = 0;
         inet_csk(sk)->icsk_backoff = 0;
  }

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