Messages in this thread Patch in this message | | | Date | Fri, 21 Nov 2008 15:07:32 +0200 (EET) | From | "Ilpo Järvinen" <> | Subject | [PATCH] tcp: fix potential corner case issue in segmentation (Was: Re: [PATCH] Do not use TSO/GSO when there is urgent data) |
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On Fri, 21 Nov 2008, Petr Tesarik wrote:
> This patch fixes http://bugzilla.kernel.org/show_bug.cgi?id=12014 > > Since most (if not all) implementations of TSO and even the in-kernel > software GSO do not update the urgent pointer when splitting a large > segment, it is necessary to turn off TSO/GSO for all outgoing traffic > with the URG pointer set.
Good observation, I totally missed this possibility of T/GSO while looking.
> Looking at tcp_current_mss (and the preceding comment) I even think > this was the original intention. However, this approach is insufficient, > because TSO/GSO is turned off only for newly created frames, not for > frames which were already pending at the arrival of a message with > MSG_OOB set. These frames were created when TSO/GSO was enabled, > so they may be large, and they will have the urgent pointer set > in tcp_transmit_skb(). > > With this patch, such large packets will be fragmented again before > going to the transmit routine.
I wonder if there's some corner case which still fails to fragment in tcp_retransmit_xmit's in skb->len <= cur_mss case if cur_mss grew very recently (and therefore skb-len now fits to a single segment).
Patch below, changed subject is due to patchwork as requested by DaveM (if you'd find that strange).
> As a side note, at least the following NICs are known to screw up > the urgent pointer in the TCP header when doing TSO: > > Intel 82566MM (PCI ID 8086:1049) > Intel 82566DC (PCI ID 8086:104b) > Intel 82541GI (PCI ID 8086:1076) > Broadcom NetXtreme II BCM5708 (PCI ID 14e4:164c)
Heh, it might already be longer than the list we would get from the working ones. Not very likely too many people consider urg too seriously to get it right.
> Signed-off-by: Petr Tesarik <ptesarik@suse.cz> > CC: Jan Sembera <jsembera@suse.cz> > CC: Ilpo Jarvinen <ilpo.jarvinen@helsinki.fi> > > -- > tcp_output.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c > --- a/net/ipv4/tcp_output.c > +++ b/net/ipv4/tcp_output.c > @@ -722,7 +722,8 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff > *skb) > static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, > unsigned int mss_now) > { > - if (skb->len <= mss_now || !sk_can_gso(sk)) { > + if (skb->len <= mss_now || !sk_can_gso(sk) || > + tcp_urg_mode(tcp_sk(sk))) { > /* Avoid the costly divide in the normal > * non-TSO case. > */ > @@ -1163,7 +1164,9 @@ static int tcp_init_tso_segs(struct sock *sk, struct > sk_buff *skb, > { > int tso_segs = tcp_skb_pcount(skb); > > - if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) { > + if (!tso_segs || > + (tso_segs > 1 && (tcp_skb_mss(skb) != mss_now || > + tcp_urg_mode(tcp_sk(sk))))) { > tcp_set_skb_tso_segs(sk, skb, mss_now); > tso_segs = tcp_skb_pcount(skb); > }
It's a bit intrusive but I couldn't immediately come up with alternative that would have worked (came up with some not working ones :-)).
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
-- i.
--
[PATCH] tcp: fix potential corner case issue in segmentation
If cur_mss grew very recently so that the previously G/TSOed skb now fits well into a single segment, it might get send up in parts unless we calculate # of segments again. Whether it actually would break something more than that I don't know. But this would create a more significant problem with the urg t/gso problem that was found by Petr Tesarik <ptesarik@suse.cz>.
Compile tested only.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> --- net/ipv4/tcp_output.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index a524627..129f46b 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1944,6 +1944,8 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) if (skb->len > cur_mss) { if (tcp_fragment(sk, skb, cur_mss, cur_mss)) return -ENOMEM; /* We'll try again later. */ + } else { + tcp_init_tso_segs(sk, skb, cur_mss); } /* Collapse two adjacent packets if worthwhile and we can. */ -- 1.5.2.2 | |