Re: [RFC PATCH v2 net-next 4/4] tcp: change SYN ACK retransmit behaviour to account for rehash
From: Eric Dumazet <edumazet@google.com>
Date: 2021-12-02 17:24:24
On Thu, Dec 2, 2021 at 8:41 AM Akhmat Karakotov [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Disabling rehash behavior did not affect SYN ACK retransmits because hash was forcefully changed bypassing the sk_rethink_hash function. This patch adds a condition which checks for rehash mode before resetting hash. Signed-off-by: Akhmat Karakotov <redacted> --- net/ipv4/tcp_output.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 6d72f3ea48c4..7d54bbe00cde 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c@@ -4108,7 +4108,8 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req) struct flowi fl; int res; - tcp_rsk(req)->txhash = net_tx_rndhash(); + if (sk->sk_txrehash == SOCK_TXREHASH_ENABLED)
Since you add a new sk->sk_txrehash, you probably want to add
READ_ONCE()/WRITE_ONCE() over the reads/writes,
because at this point the listener socket lock is not held.
/* Paired with WRITE_ONCE() in sock_setsockopt() */
if (READ_ONCE(sk->sk_txrehash) == SOCK_TXREHASH_ENABLED)
sock_setsockopt() would need a similar comment
/* Paired with READ_ONCE() in tcp_rtx_synack() */
WRITE_ONCE(sk->sk_txrehash, val);
+ tcp_rsk(req)->txhash = net_tx_rndhash();
res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL,
NULL);
if (!res) {
--
2.17.1