linux-kernel - [PATCH net] net/smc: avoid overwriting when adjusting sock bufsizes

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Date: Fri, 31 May 2024 16:54:17 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: gbayer@...ux.ibm.com,
	wenjia@...ux.ibm.com,
	jaka@...ux.ibm.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: alibuda@...ux.alibaba.com,
	tonylu@...ux.alibaba.com,
	guwen@...ux.alibaba.com,
	linux-s390@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net] net/smc: avoid overwriting when adjusting sock bufsizes

When copying smc settings to clcsock, avoid setting clcsock's sk_sndbuf
to sysctl_tcp_wmem[1], since this may overwrite the value set by
tcp_sndbuf_expand() in TCP connection establishment.

And the other setting sk_{snd|rcv}buf to sysctl value in
smc_adjust_sock_bufsizes() can also be omitted since the initialization
of smc sock and clcsock has set sk_{snd|rcv}buf to smc.sysctl_{w|r}mem
or ipv4_sysctl_tcp_{w|r}mem[1].

Fixes: 30c3c4a4497c ("net/smc: Use correct buffer sizes when switching between TCP and SMC")
Link: https://lore.kernel.org/r/5eaf3858-e7fd-4db8-83e8-3d7a3e0e9ae2@linux.alibaba.com
Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
---
FYI,
The detailed motivation and testing can be found in the link above.
---
 net/smc/af_smc.c | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 9389f0cfa374..a35281153067 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -459,29 +459,11 @@ static int smc_bind(struct socket *sock, struct sockaddr *uaddr,
 static void smc_adjust_sock_bufsizes(struct sock *nsk, struct sock *osk,
 				     unsigned long mask)
 {
-	struct net *nnet = sock_net(nsk);
-
 	nsk->sk_userlocks = osk->sk_userlocks;
-	if (osk->sk_userlocks & SOCK_SNDBUF_LOCK) {
+	if (osk->sk_userlocks & SOCK_SNDBUF_LOCK)
 		nsk->sk_sndbuf = osk->sk_sndbuf;
-	} else {
-		if (mask == SK_FLAGS_SMC_TO_CLC)
-			WRITE_ONCE(nsk->sk_sndbuf,
-				   READ_ONCE(nnet->ipv4.sysctl_tcp_wmem[1]));
-		else
-			WRITE_ONCE(nsk->sk_sndbuf,
-				   2 * READ_ONCE(nnet->smc.sysctl_wmem));
-	}
-	if (osk->sk_userlocks & SOCK_RCVBUF_LOCK) {
+	if (osk->sk_userlocks & SOCK_RCVBUF_LOCK)
 		nsk->sk_rcvbuf = osk->sk_rcvbuf;
-	} else {
-		if (mask == SK_FLAGS_SMC_TO_CLC)
-			WRITE_ONCE(nsk->sk_rcvbuf,
-				   READ_ONCE(nnet->ipv4.sysctl_tcp_rmem[1]));
-		else
-			WRITE_ONCE(nsk->sk_rcvbuf,
-				   2 * READ_ONCE(nnet->smc.sysctl_rmem));
-	}
 }
 
 static void smc_copy_sock_settings(struct sock *nsk, struct sock *osk,
-- 
2.32.0.3.g01195cf9f