From: Vitaliy Makkoveev <mvs@openbsd.org>
Subject: Re: tcp, sysctl: unlock TCPCTL_REASS_LIMIT and TCPCTL_SACKHOLE_LIMIT
To: Alexander Bluhm <bluhm@openbsd.org>, tech@openbsd.org
Date: Tue, 13 May 2025 13:45:36 +0300

On Sat, May 10, 2025 at 08:00:27AM +0300, Vitaliy Makkoveev wrote:
> They are identical, so unlock them both. The temporary `tcp_sysctl_lock'
> and the pool_sethardlimit() serialization are useless because we are
> serialized with sysctl_lock rwlock(9). However I want to do this
> serialization for consistency reason. I will replace `tcp_sysctl_lock'
> with `sysctl_lock' after tcp_sysctl() unlocked.
> 

Updated against the latest sources. Now all TCP sysctl variables became
mp-safe, so unlock tcp_sysctl() too.

Index: sys/netinet/in_proto.c
===================================================================
RCS file: /cvs/src/sys/netinet/in_proto.c,v
diff -u -p -r1.122 in_proto.c
--- sys/netinet/in_proto.c	26 Apr 2025 13:58:08 -0000	1.122
+++ sys/netinet/in_proto.c	13 May 2025 10:40:29 -0000
@@ -198,7 +198,7 @@ const struct protosw inetsw[] = {
   .pr_domain	= &inetdomain,
   .pr_protocol	= IPPROTO_TCP,
   .pr_flags	= PR_CONNREQUIRED|PR_WANTRCVD|PR_ABRTACPTDIS|PR_SPLICE|
-		    PR_MPINPUT,
+		    PR_MPINPUT|PR_MPSYSCTL,
   .pr_input	= tcp_input,
   .pr_ctlinput	= tcp_ctlinput,
   .pr_ctloutput	= tcp_ctloutput,
Index: sys/netinet/tcp_usrreq.c
===================================================================
RCS file: /cvs/src/sys/netinet/tcp_usrreq.c,v
diff -u -p -r1.246 tcp_usrreq.c
--- sys/netinet/tcp_usrreq.c	13 May 2025 09:17:41 -0000	1.246
+++ sys/netinet/tcp_usrreq.c	13 May 2025 10:40:29 -0000
@@ -1460,29 +1460,38 @@ tcp_sysctl(int *name, u_int namelen, voi
 		return tcp_ident(oldp, oldlenp, newp, newlen, 1);
 
 	case TCPCTL_REASS_LIMIT:
-		NET_LOCK();
-		nval = tcp_reass_limit;
-		error = sysctl_int(oldp, oldlenp, newp, newlen, &nval);
-		if (!error && nval != tcp_reass_limit) {
-			error = pool_sethardlimit(&tcpqe_pool, nval, NULL, 0);
-			if (!error)
-				tcp_reass_limit = nval;
+	case TCPCTL_SACKHOLE_LIMIT: {
+		struct pool *pool;
+		int *var;
+
+		if (name[0] == TCPCTL_REASS_LIMIT) {
+			pool = &tcpqe_pool;
+			var = &tcp_reass_limit;
+		} else {
+			pool = &sackhl_pool;
+			var = &tcp_sackhole_limit;
 		}
-		NET_UNLOCK();
-		return (error);
 
-	case TCPCTL_SACKHOLE_LIMIT:
-		NET_LOCK();
-		nval = tcp_sackhole_limit;
+		oval = nval = atomic_load_int(var);
 		error = sysctl_int(oldp, oldlenp, newp, newlen, &nval);
-		if (!error && nval != tcp_sackhole_limit) {
-			error = pool_sethardlimit(&sackhl_pool, nval, NULL, 0);
-			if (!error)
-				tcp_sackhole_limit = nval;
+
+		if (error == 0 && oval != nval) {
+			extern struct rwlock sysctl_lock;
+
+			error = rw_enter(&sysctl_lock, RW_WRITE | RW_INTR);
+			if (error)
+				return (error);
+			if (nval != atomic_load_int(var)) {
+				error = pool_sethardlimit(pool, nval,
+				    NULL, 0);
+				if (error == 0)
+					atomic_store_int(var, nval);
+			}
+			rw_exit(&sysctl_lock);
 		}
-		NET_UNLOCK();
-		return (error);
 
+		return (error);
+	}
 	case TCPCTL_STATS:
 		return (tcp_sysctl_tcpstat(oldp, oldlenp, newp));
 
Index: sys/netinet6/in6_proto.c
===================================================================
RCS file: /cvs/src/sys/netinet6/in6_proto.c,v
diff -u -p -r1.125 in6_proto.c
--- sys/netinet6/in6_proto.c	26 Apr 2025 13:58:08 -0000	1.125
+++ sys/netinet6/in6_proto.c	13 May 2025 10:40:29 -0000
@@ -148,7 +148,7 @@ const struct protosw inet6sw[] = {
   .pr_domain	= &inet6domain,
   .pr_protocol	= IPPROTO_TCP,
   .pr_flags	= PR_CONNREQUIRED|PR_WANTRCVD|PR_ABRTACPTDIS|PR_SPLICE|
-		    PR_MPINPUT,
+		    PR_MPINPUT|PR_MPSYSCTL,
   .pr_input	= tcp_input,
   .pr_ctlinput	= tcp6_ctlinput,
   .pr_ctloutput	= tcp_ctloutput,