netdev - [PATCH 2.6.23-rc9] [TCP]: Fix fastpath_cnt_hint when GSO skb is partially ACKed

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Message-ID: <Pine.LNX.4.64.0710042330140.17406@kivilampi-30.cs.helsinki.fi>
Date:	Thu, 4 Oct 2007 23:38:24 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>, Cedric Le Goater <clg@...ibm.com>
Subject: [PATCH 2.6.23-rc9] [TCP]: Fix fastpath_cnt_hint when GSO skb is
 partially ACKed

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@...ibm.com>

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
---

Dave, here's the same fix to upcoming 2.6.23, hopefully it can
make it in time. Probably minor enough to skip stable-2.6.22,
especially since 2.6.23 is soooo close :-), but I leave that
up to you.

 net/ipv4/tcp_input.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bbad2cd..f893e90 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2420,6 +2420,9 @@ 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);
-- 
1.5.0.6