Fix TCP's ->fastpath_cnt_hit handling.

changeset 48611c47d09023d9356e78550d1cadb8d61da9c8 in mainline.

When only GSO skb was partially ACKed, no hints are reset,
therefore fastpath_cnt_hint must be tweaked too or else it can
corrupt fackets_out. The corruption to occur, one must have
non-trivial ACK/SACK sequence, so this bug is not very often
that harmful. There's a fackets_out state reset in TCP because
fackets_out is known to be inaccurate and that fixes the issue
eventually anyway.

In case there was also at least one skb that got fully ACKed,
the fastpath_skb_hint is set to NULL which causes a recount for
fastpath_cnt_hint (the old value won't be accessed anymore),
thus it can safely be decremented without additional checking.

Reported by Cedric Le Goater <clg@fr.ibm.com>

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5bfda70a6a564a060181c6c5cfe0a8b3b0879b3e..e33fb3d0b8cc895c75f062a0b78c87e6fea8d380 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2403,6 +2403,9 @@ static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
                        __u32 dval = min(tp->fackets_out, packets_acked);
                        tp->fackets_out -= dval;
                }
+               /* hint's skb might be NULL but we don't need to care */
+               tp->fastpath_cnt_hint -= min_t(u32, packets_acked,
+                                              tp->fastpath_cnt_hint);
                tp->packets_out -= packets_acked;
 
                BUG_ON(tcp_skb_pcount(skb) == 0);