Remove a useless kernel lock from the TCP socket splicing path.

When send buffer space in the drain socket becomes available, a
task is added to move data, and also the userland was informed.
The latter is not usefull as this would mix a kernel and user stream.
So programs do not wait for this event.  Avoid calling sowakeup()
from sowwakeup(), this also reduces grabing the kernel lock.  Instead
inform the userland about the write event when the splicing is
dissolved in sounsplice().
OK claudio@

1 files changed, 27 insertions, 11 deletions

diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
index 802bf361a45..6989510287a 100644
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uipc_socket.c,v 1.231 2018/12/17 16:46:59 bluhm Exp $	*/
+/*	$OpenBSD: uipc_socket.c,v 1.232 2019/07/04 17:42:17 bluhm Exp $	*/
 /*	$NetBSD: uipc_socket.c,v 1.21 1996/02/04 02:17:52 christos Exp $	*/
 
 /*
@@ -195,6 +195,8 @@ solisten(struct socket *so, int backlog)
 	return (0);
 }
 
+#define SOSP_FREEING_READ	1
+#define SOSP_FREEING_WRITE	2
 void
 sofree(struct socket *so, int s)
 {
@@ -218,11 +220,20 @@ sofree(struct socket *so, int s)
 	sigio_free(&so->so_sigio);
 #ifdef SOCKET_SPLICE
 	if (so->so_sp) {
-		if (issplicedback(so))
-			sounsplice(so->so_sp->ssp_soback, so,
-			    so->so_sp->ssp_soback != so);
-		if (isspliced(so))
-			sounsplice(so, so->so_sp->ssp_socket, 0);
+		if (issplicedback(so)) {
+			int freeing = SOSP_FREEING_WRITE;
+
+			if (so->so_sp->ssp_soback == so)
+				freeing |= SOSP_FREEING_READ;
+			sounsplice(so->so_sp->ssp_soback, so, freeing);
+		}
+		if (isspliced(so)) {
+			int freeing = SOSP_FREEING_READ;
+
+			if (so == so->so_sp->ssp_socket)
+				freeing |= SOSP_FREEING_WRITE;
+			sounsplice(so, so->so_sp->ssp_socket, freeing);
+		}
 	}
 #endif /* SOCKET_SPLICE */
 	sbrelease(so, &so->so_snd);
@@ -1148,7 +1159,7 @@ sosplice(struct socket *so, int fd, off_t max, struct timeval *tv)
 			return (error);
 		}
 		if (so->so_sp->ssp_socket)
-			sounsplice(so, so->so_sp->ssp_socket, 1);
+			sounsplice(so, so->so_sp->ssp_socket, 0);
 		sbunlock(so, &so->so_rcv);
 		return (0);
 	}
@@ -1227,7 +1238,7 @@ sosplice(struct socket *so, int fd, off_t max, struct timeval *tv)
 }
 
 void
-sounsplice(struct socket *so, struct socket *sosp, int wakeup)
+sounsplice(struct socket *so, struct socket *sosp, int freeing)
 {
 	soassertlocked(so);
 
@@ -1236,8 +1247,11 @@ sounsplice(struct socket *so, struct socket *sosp, int wakeup)
 	sosp->so_snd.sb_flags &= ~SB_SPLICE;
 	so->so_rcv.sb_flags &= ~SB_SPLICE;
 	so->so_sp->ssp_socket = sosp->so_sp->ssp_soback = NULL;
-	if (wakeup && soreadable(so))
+	/* Do not wakeup a socket that is about to be freed. */
+	if ((freeing & SOSP_FREEING_READ) == 0 && soreadable(so))
 		sorwakeup(so);
+	if ((freeing & SOSP_FREEING_WRITE) == 0 && sowriteable(sosp))
+		sowwakeup(sosp);
 }
 
 void
@@ -1249,7 +1263,7 @@ soidle(void *arg)
 	s = solock(so);
 	if (so->so_rcv.sb_flags & SB_SPLICE) {
 		so->so_error = ETIMEDOUT;
-		sounsplice(so, so->so_sp->ssp_socket, 1);
+		sounsplice(so, so->so_sp->ssp_socket, 0);
 	}
 	sounlock(so, s);
 }
@@ -1574,7 +1588,7 @@ somove(struct socket *so, int wait)
 		so->so_error = error;
 	if (((so->so_state & SS_CANTRCVMORE) && so->so_rcv.sb_cc == 0) ||
 	    (sosp->so_state & SS_CANTSENDMORE) || maxreached || error) {
-		sounsplice(so, sosp, 1);
+		sounsplice(so, sosp, 0);
 		return (0);
 	}
 	if (timerisset(&so->so_idletv))
@@ -1620,6 +1634,8 @@ sowwakeup(struct socket *so)
 #ifdef SOCKET_SPLICE
 	if (so->so_snd.sb_flags & SB_SPLICE)
 		task_add(sosplice_taskq, &so->so_sp->ssp_soback->so_splicetask);
+	if (issplicedback(so))
+		return;
 #endif
 	sowakeup(so, &so->so_snd);
 }