sockets: retire sorflush()

With removal of dom_dispose method the function boils down to two
meaningful function calls: socantrcvmore() and sbrelease().  The latter is
only relevant for protocols that use generic socket buffers.

The socket I/O sx(9) lock acquisition in sorflush() is not relevant for
shutdown(2) operation as it doesn't do any I/O that may interleave with
read(2) or write(2).  The socket buffer mutex acquisition inside
sbrelease() is what guarantees thread safety.  This sx(9) acquisition in
soshutdown() can be tracked down to 4.4BSD times, where it used to be
sblock(), and it was carried over through the years evolving together with
sockets with no reconsideration of why do we carry it over.  I can't tell
if that sblock() made sense back then, but it doesn't make any today.

Reviewed by:		tuexen
Differential Revision:	https://reviews.freebsd.org/D43415

8 files changed, 24 insertions, 49 deletions

diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
index 1626c6a7442d..65230e39e4ae 100644
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -95,9 +95,9 @@
  *
  * NOTE: With regard to VNETs the general rule is that callers do not set
  * curvnet. Exceptions to this rule include soabort(), sodisconnect(),
- * sofree() (and with that sorele(), sotryfree()), as well as sonewconn()
- * and sorflush(), which are usually called from a pre-set VNET context.
- * sopoll() currently does not need a VNET context to be set.
+ * sofree() (and with that sorele(), sotryfree()), as well as sonewconn(),
+ * which are usually called from a pre-set VNET context. sopoll() currently
+ * does not need a VNET context to be set.
  */
 
 #include <sys/cdefs.h>
@@ -2972,36 +2972,6 @@ soshutdown(struct socket *so, enum shutdown_how how)
 }
 
 /*
- * Used by several pr_shutdown implementations that use generic socket buffers.
- */
-void
-sorflush(struct socket *so)
-{
-	int error;
-
-	VNET_SO_ASSERT(so);
-
-	/*
-	 * Dislodge threads currently blocked in receive and wait to acquire
-	 * a lock against other simultaneous readers before clearing the
-	 * socket buffer.  Don't let our acquire be interrupted by a signal
-	 * despite any existing socket disposition on interruptable waiting.
-	 */
-	socantrcvmore(so);
-
-	error = SOCK_IO_RECV_LOCK(so, SBL_WAIT | SBL_NOINTR);
-	if (error != 0) {
-		KASSERT(SOLISTENING(so),
-		    ("%s: soiolock(%p) failed", __func__, so));
-		return;
-	}
-
-	sbrelease(so, SO_RCV);
-	SOCK_IO_RECV_UNLOCK(so);
-
-}
-
-/*
  * Wrapper for Socket established helper hook.
  * Parameters: socket, context of the hook point, hook id.
  */
diff --git a/sys/net/rtsock.c b/sys/net/rtsock.c
index 94d5e9e4bccc..cb149f176b6d 100644
--- a/sys/net/rtsock.c
+++ b/sys/net/rtsock.c
@@ -457,10 +457,12 @@ rts_shutdown(struct socket *so, enum shutdown_how how)
 	 */
 	switch (how) {
 	case SHUT_RD:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		break;
 	case SHUT_RDWR:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		/* FALLTHROUGH */
 	case SHUT_WR:
 		socantsendmore(so);
diff --git a/sys/netinet/raw_ip.c b/sys/netinet/raw_ip.c
index a6bef1c7e275..004aaea01bfa 100644
--- a/sys/netinet/raw_ip.c
+++ b/sys/netinet/raw_ip.c
@@ -994,10 +994,12 @@ rip_shutdown(struct socket *so, enum shutdown_how how)
 
 	switch (how) {
 	case SHUT_RD:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		break;
 	case SHUT_RDWR:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		/* FALLTHROUGH */
 	case SHUT_WR:
 		socantsendmore(so);
diff --git a/sys/netinet/sctp_usrreq.c b/sys/netinet/sctp_usrreq.c
index ec9f211b519b..51c056e052a5 100644
--- a/sys/netinet/sctp_usrreq.c
+++ b/sys/netinet/sctp_usrreq.c
@@ -868,11 +868,7 @@ sctp_shutdown(struct socket *so, enum shutdown_how how)
 			SCTP_TCB_UNLOCK(stcb);
 		}
 		SCTP_INP_WUNLOCK(inp);
-		/*
-		 * XXXGL: does SCTP need sorflush()? This is what old
-		 * soshutdown() used to do for all kinds of sockets.
-		 */
-		sorflush(so);
+		socantrcvmore(so);
 		if (how == SHUT_RD)
 			break;
 		/* FALLTHROUGH */
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index ccd6a6149dae..7c8e3d7e72db 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -824,10 +824,12 @@ tcp_usr_shutdown(struct socket *so, enum shutdown_how how)
 
 	switch (how) {
 	case SHUT_RD:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		break;
 	case SHUT_RDWR:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		/* FALLTHROUGH */
 	case SHUT_WR:
 		/*
diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
index f91a96edeb68..b68ec95a923a 100644
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -1696,10 +1696,12 @@ udp_shutdown(struct socket *so, enum shutdown_how how)
 
 	switch (how) {
 	case SHUT_RD:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		break;
 	case SHUT_RDWR:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		/* FALLTHROUGH */
 	case SHUT_WR:
 		socantsendmore(so);
diff --git a/sys/netinet6/raw_ip6.c b/sys/netinet6/raw_ip6.c
index 3264de331817..5b31a84f31eb 100644
--- a/sys/netinet6/raw_ip6.c
+++ b/sys/netinet6/raw_ip6.c
@@ -839,10 +839,12 @@ rip6_shutdown(struct socket *so, enum shutdown_how how)
 
 	switch (how) {
 	case SHUT_RD:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		break;
 	case SHUT_RDWR:
-		sorflush(so);
+		socantrcvmore(so);
+		sbrelease(so, SO_RCV);
 		/* FALLTHROUGH */
 	case SHUT_WR:
 		socantsendmore(so);
diff --git a/sys/sys/socketvar.h b/sys/sys/socketvar.h
index 19ca52177d17..5d651b36b1e7 100644
--- a/sys/sys/socketvar.h
+++ b/sys/sys/socketvar.h
@@ -501,7 +501,6 @@ int	soreceive_generic(struct socket *so, struct sockaddr **paddr,
 void	sorele_locked(struct socket *so);
 void	sodealloc(struct socket *);
 int	soreserve(struct socket *so, u_long sndcc, u_long rcvcc);
-void	sorflush(struct socket *so);
 int	sosend(struct socket *so, struct sockaddr *addr, struct uio *uio,
 	    struct mbuf *top, struct mbuf *control, int flags,
 	    struct thread *td);