[TCP]: Adjust Reno SACK estimate in tcp_fragment
Since the introduction of TSO pcount a year ago, it has been possible
for tcp_fragment() to cause packets_out to decrease. Prior to that,
tcp_retrans_try_collapse() was the only way for that to happen on the
retransmission path.
When this happens with Reno, it is possible for sasked_out to become
invalid because it is only an estimate and not tied to any particular
packet on the retransmission queue.
Therefore we need to adjust sacked_out as well as left_out in the Reno
case. The following patch does exactly that.
This bug is pretty difficult to trigger in practice though since you
need a SACKless peer with a retransmission that occurs just as the
cached MTU value expires.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5dd6dd7..d6e3d26 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -509,7 +509,16 @@
tp->lost_out -= diff;
tp->left_out -= diff;
}
+
if (diff > 0) {
+ /* Adjust Reno SACK estimate. */
+ if (!tp->rx_opt.sack_ok) {
+ tp->sacked_out -= diff;
+ if ((int)tp->sacked_out < 0)
+ tp->sacked_out = 0;
+ tcp_sync_left_out(tp);
+ }
+
tp->fackets_out -= diff;
if ((int)tp->fackets_out < 0)
tp->fackets_out = 0;