On Tue, 13 Nov 2007, David Miller wrote:
> From: "Ilpo_Järvinen" <[EMAIL PROTECTED]>
> Date: Tue, 13 Nov 2007 23:35:39 +0200 (EET)
>
> > [PATCH] [TCP] FRTO: Plug potential LOST-bit leak
> >
> > It might be possible that, in some extreme scenario that
> > I just cannot now construct in my mind, end_seq <=
> > frto_highmark check does not match causing the lost_out
> > and LOST bits become out-of-sync due to clearing and
> > recounting in the loop.
> >
> > This may fix LOST-bit leak reported by Chazarain Guillaume
> > <[EMAIL PROTECTED]>.
> >
> > Signed-off-by: Ilpo Järvinen <[EMAIL PROTECTED]>
>
> This patch looks correct to me, so I added it to net-2.6
>
> Chazarain please let us know if it does indeed cure your
> problem.
Ok, now after one night more, I think I know what it was, this
indeed "cured" it (and IMHO we can leave it there too).
...But here's a fix that very well explains why the frto_highmark
check could give a bit strange results :-).
--
[PATCH] [TCP] FRTO: Clear frto_highmark only after process_frto that uses it
I broke this in commit 3de96471bd7fb76406e975ef6387abe3a0698149.
tcp_process_frto should always see a valid frto_highmark. An
invalid frto_highmark (zero) is very likely what ultimately
caused a seqno compare in tcp_frto_enter_loss to do the wrong
leading to the LOST-bit leak.
Having LOST-bits integry ensured like done after commit
23aeeec365dcf8bc87fae44c533e50d0bb4f23cc won't hurt. It may
still be useful in some other, possibly legimate, scenario.
Reported by Chazarain Guillaume <[EMAIL PROTECTED]>.
Signed-off-by: Ilpo Järvinen <[EMAIL PROTECTED]>
---
net/ipv4/tcp_input.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3f126ec..0f0c1c9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3113,11 +3113,11 @@ static int tcp_ack(struct sock *sk, struct sk_buff
*skb, int flag)
/* See if we can take anything off of the retransmit queue. */
flag |= tcp_clean_rtx_queue(sk, &seq_rtt, prior_fackets);
+ if (tp->frto_counter)
+ frto_cwnd = tcp_process_frto(sk, flag);
/* Guarantee sacktag reordering detection against wrap-arounds */
if (before(tp->frto_highmark, tp->snd_una))
tp->frto_highmark = 0;
- if (tp->frto_counter)
- frto_cwnd = tcp_process_frto(sk, flag);
if (tcp_ack_is_dubious(sk, flag)) {
/* Advance CWND, if state allows this. */
--
1.5.0.6
