tcp_skb_can_collapse() checks for conditions which don't make
sense on input. Because of this we ended up sprinkling a few
pairs of mptcp_skb_can_collapse() and skb_cmp_decrypted() calls
on the input path. Group them in a new helper. This should make
it less likely that someone will check mptcp and not decrypted
or vice versa when adding new code.
This implicitly adds a decrypted check early in tcp_collapse().
AFAIU this will very slightly increase our ability to collapse
packets under memory pressure, not a real bug.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
include/net/tcp.h | 7 +++++++
net/ipv4/tcp_input.c | 11 +++--------
net/ipv4/tcp_ipv4.c | 3 +--
3 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 32815a40dea1..32741856da01 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1071,6 +1071,13 @@ static inline bool tcp_skb_can_collapse(const struct sk_buff *to,
skb_pure_zcopy_same(to, from));
}
+static inline bool tcp_skb_can_collapse_rx(const struct sk_buff *to,
+ const struct sk_buff *from)
+{
+ return likely(mptcp_skb_can_collapse(to, from) &&
+ !skb_cmp_decrypted(to, from));
+}
+
/* Events passed to congestion control interface */
enum tcp_ca_event {
CA_EVENT_TX_START, /* first transmit when no packets in flight */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5aadf64e554d..212b6fd0caf7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4813,10 +4813,7 @@ static bool tcp_try_coalesce(struct sock *sk,
if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
return false;
- if (!mptcp_skb_can_collapse(to, from))
- return false;
-
- if (skb_cmp_decrypted(from, to))
+ if (!tcp_skb_can_collapse_rx(to, from))
return false;
if (!skb_try_coalesce(to, from, fragstolen, &delta))
@@ -5372,7 +5369,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
break;
}
- if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
+ if (n && n != tail && tcp_skb_can_collapse_rx(skb, n) &&
TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
end_of_skbs = false;
break;
@@ -5423,11 +5420,9 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
skb = tcp_collapse_one(sk, skb, list, root);
if (!skb ||
skb == tail ||
- !mptcp_skb_can_collapse(nskb, skb) ||
+ !tcp_skb_can_collapse_rx(nskb, skb) ||
(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
goto end;
- if (skb_cmp_decrypted(skb, nskb))
- goto end;
}
}
}
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 041c7eda9abe..228de0c95a9d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2049,8 +2049,7 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb,
TCP_SKB_CB(skb)->tcp_flags) & TCPHDR_ACK) ||
((TCP_SKB_CB(tail)->tcp_flags ^
TCP_SKB_CB(skb)->tcp_flags) & (TCPHDR_ECE | TCPHDR_CWR)) ||
- !mptcp_skb_can_collapse(tail, skb) ||
- skb_cmp_decrypted(tail, skb) ||
+ !tcp_skb_can_collapse_rx(tail, skb) ||
thtail->doff != th->doff ||
memcmp(thtail + 1, th + 1, hdrlen - sizeof(*th)))
goto no_coalesce;
--
2.45.1
Jakub Kicinski wrote: > tcp_skb_can_collapse() checks for conditions which don't make > sense on input. Because of this we ended up sprinkling a few > pairs of mptcp_skb_can_collapse() and skb_cmp_decrypted() calls > on the input path. Group them in a new helper. This should make > it less likely that someone will check mptcp and not decrypted > or vice versa when adding new code. > > This implicitly adds a decrypted check early in tcp_collapse(). > AFAIU this will very slightly increase our ability to collapse > packets under memory pressure, not a real bug. > > Signed-off-by: Jakub Kicinski <kuba@kernel.org> Reviewed-by: Willem de Bruijn <willemb@google.com>
Hi Jakub, On 31/05/2024 01:36, Jakub Kicinski wrote: > tcp_skb_can_collapse() checks for conditions which don't make > sense on input. Because of this we ended up sprinkling a few > pairs of mptcp_skb_can_collapse() and skb_cmp_decrypted() calls > on the input path. Group them in a new helper. This should make > it less likely that someone will check mptcp and not decrypted > or vice versa when adding new code. > > This implicitly adds a decrypted check early in tcp_collapse(). > AFAIU this will very slightly increase our ability to collapse > packets under memory pressure, not a real bug. Good idea! Thank you for this refactoring, and for having cc'd MPTCP ML: Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Cheers, Matt -- Sponsored by the NGI0 Core fund.
On Fri, May 31, 2024 at 1:36 AM Jakub Kicinski <kuba@kernel.org> wrote: > > tcp_skb_can_collapse() checks for conditions which don't make > sense on input. Because of this we ended up sprinkling a few > pairs of mptcp_skb_can_collapse() and skb_cmp_decrypted() calls > on the input path. Group them in a new helper. This should make > it less likely that someone will check mptcp and not decrypted > or vice versa when adding new code. > > This implicitly adds a decrypted check early in tcp_collapse(). > AFAIU this will very slightly increase our ability to collapse > packets under memory pressure, not a real bug. > > Signed-off-by: Jakub Kicinski <kuba@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com>
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