Hello,
While testing a failover scenario, I managed to trigger an ack storm
between a Linux box and another system. Although the cause of this particular
ACK storm was due to the other box forgetting that it sent out a FIN (the
second node was unaware of the FIN the first sent in its dying gasp, which
is what I'm trying to fix, but it's a tricky race), the resulting Linux
behaviour wasn't very robust. Is there any particularly good reason that
FIN flag gets cleared on a connection which is being shut down? The trace
that motivates this can be seen at
http://www.kvack.org/~bcrl/ack-storm.log . As near as I can tell, a
similar effect can occur between two Linux boxes if the right packets get
reordered/dropped during connection teardown.
-ben
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0faacf9..1e54291 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -635,9 +635,9 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32
len, unsigned int mss
TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
- /* PSH and FIN should only be set in the second packet. */
+ /* PSH should only be set in the second packet. */
flags = TCP_SKB_CB(skb)->flags;
- TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
+ TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_PSH);
TCP_SKB_CB(buff)->flags = flags;
TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL;
@@ -1124,9 +1124,9 @@ static int tso_fragment(struct sock *sk, struct sk_buff
*skb, unsigned int len,
TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
- /* PSH and FIN should only be set in the second packet. */
+ /* PSH should only be set in the second packet. */
flags = TCP_SKB_CB(skb)->flags;
- TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
+ TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_PSH);
TCP_SKB_CB(buff)->flags = flags;
/* This packet was never sent out yet, so no SACK bits. */
@@ -1308,7 +1308,7 @@ static int tcp_mtu_probe(struct sock *sk)
sk_stream_free_skb(sk, skb);
} else {
TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
-
~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
+ ~(TCPCB_FLAG_PSH);
if (!skb_shinfo(skb)->nr_frags) {
skb_pull(skb, copy);
if (skb->ip_summed != CHECKSUM_PARTIAL)
-
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