Revert prev commit, spoke too soon, close race condition came back.

servers/slapd/connection.c

@@ -43,10 +43,33 @@
 #include "slapi/slapi.h"
 #endif
 
+#ifdef SLAP_MULTI_CONN_ARRAY
+/* for Multiple Connection Arrary (MCA) Support */
+static ldap_pvt_thread_mutex_t* connections_mutex;
+static Connection **connections = NULL;
+
+/* set to the number of processors (round up to a power of 2) */
+#	define NUM_CONNECTION_ARRAY 4
+
+/* partition the array in a modulo manner */
+#	define MCA_conn_array_id(fd)		((int)(fd)%NUM_CONNECTION_ARRAY)
+#	define MCA_conn_array_element_id(fd)	((int)(fd)/NUM_CONNECTION_ARRAY)
+#	define MCA_ARRAY_SIZE			((int)(MCA_conn_array_element_id(dtblsize) + (MCA_conn_array_id(dtblsize) ? 1 : 0)))
+#	define MCA_conn_check(fd)		(dtblsize > 0 && (fd) >= 0 && (fd) < (MCA_ARRAY_SIZE*NUM_CONNECTION_ARRAY))
+#	define MCA_GET_CONNECTION(fd) (&(connections[MCA_conn_array_id(fd)]) \
+		[MCA_conn_array_element_id(fd)])
+#	define MCA_GET_CONN_MUTEX(fd) (&connections_mutex[MCA_conn_array_id(fd)])
+
+#else
 /* protected by connections_mutex */
 static ldap_pvt_thread_mutex_t connections_mutex;
 static Connection *connections = NULL;
 
+#	define MCA_conn_check(fd)		(dtblsize > 0 && (fd) < dtblsize)
+#	define MCA_GET_CONNECTION(fd) (&connections[s])
+#	define MCA_GET_CONN_MUTEX(fd) (&connections_mutex)
+#endif
+
 static ldap_pvt_thread_mutex_t conn_nextid_mutex;
 static unsigned long conn_nextid = 0;
 
@@ -56,7 +79,6 @@ static const char conn_lost_str[] = "connection lost";
 #define SLAP_C_UNINITIALIZED	0x00	/* MUST BE ZERO (0) */
 #define SLAP_C_UNUSED			0x01
 #define SLAP_C_USED				0x02
-#define	SLAP_C_PENDING			0x03
 
 /* connection state (protected by c_mutex ) */
 #define SLAP_C_INVALID			0x00	/* MUST BE ZERO (0) */
@@ -112,6 +134,69 @@ static ldap_pvt_thread_start_t connection_operation;
  * Initialize connection management infrastructure.
  */
 int connections_init(void)
+#ifdef SLAP_MULTI_CONN_ARRAY
+{
+	int		i, j;
+	Connection*	conn;
+
+	assert( connections == NULL );
+
+	if( connections != NULL) {
+		Debug( LDAP_DEBUG_ANY, "connections_init: already initialized.\n",
+			0, 0, 0 );
+		return -1;
+	}
+
+	connections_mutex = (ldap_pvt_thread_mutex_t*) ch_calloc(
+		NUM_CONNECTION_ARRAY, sizeof(ldap_pvt_thread_mutex_t) );
+	if( connections_mutex == NULL ) {
+		Debug( LDAP_DEBUG_ANY, "connections_init: "
+			"allocation of connection mutexes failed\n", 0, 0, 0 );
+		return -1;
+	}
+
+	connections = (Connection**) ch_calloc(
+		NUM_CONNECTION_ARRAY, sizeof(Connection*));
+	if( connections == NULL ) {
+		Debug( LDAP_DEBUG_ANY, "connections_init: "
+			"allocation of connection[%d] failed\n", 0, 0, 0 );
+		return -1;
+	}
+
+	for ( i = 0; i < NUM_CONNECTION_ARRAY; i++ ) {
+		ldap_pvt_thread_mutex_init( connections_mutex+i );
+		connections[i] = (Connection*) ch_calloc(
+			MCA_ARRAY_SIZE, sizeof(Connection) );
+		if( connections[i] == NULL ) {
+			Debug( LDAP_DEBUG_ANY, "connections_init: "
+				"allocation (%d*%ld) of connection array[%d] failed\n",
+				dtblsize, (long) sizeof(Connection), i );
+			return -1;
+		}
+	}
+
+	/* should check return of every call */
+	ldap_pvt_thread_mutex_init( &conn_nextid_mutex );
+
+	assert( connections[0]->c_struct_state == SLAP_C_UNINITIALIZED );
+	assert( connections[NUM_CONNECTION_ARRAY-1]->c_struct_state ==
+		SLAP_C_UNINITIALIZED );
+
+	for ( i = 0; i < NUM_CONNECTION_ARRAY; i++ ) {
+		conn = connections[i];
+		for ( j = 0; j < MCA_ARRAY_SIZE; j++ ) {
+			conn[j].c_conn_idx = j;
+		}
+	}
+
+	/*
+	 * per entry initialization of the Connection array initialization
+	 * will be done by connection_init()
+	 */ 
+
+	return 0;
+}
+#else
 {
 	int i;
 
@@ -148,12 +233,57 @@ int connections_init(void)
 
 	return 0;
 }
+#endif
 
 /*
  * Destroy connection management infrastructure.
  */
 
 int connections_destroy(void)
+#ifdef SLAP_MULTI_CONN_ARRAY
+{
+	int i;
+	ber_socket_t j;
+
+	if( connections == NULL) {
+		Debug( LDAP_DEBUG_ANY, "connections_destroy: nothing to destroy.\n",
+			0, 0, 0 );
+		return -1;
+	}
+
+    for ( i = 0; i < NUM_CONNECTION_ARRAY; i++ ) {
+		Connection* conn = connections[i];
+		for ( j = 0; j < MCA_ARRAY_SIZE; j++ ) {
+			if( conn[j].c_struct_state != SLAP_C_UNINITIALIZED ) {
+				ber_sockbuf_free( conn[j].c_sb );
+				ldap_pvt_thread_mutex_destroy( &conn[j].c_mutex );
+				ldap_pvt_thread_mutex_destroy( &conn[j].c_write_mutex );
+				ldap_pvt_thread_cond_destroy( &conn[j].c_write_cv );
+#ifdef LDAP_SLAPI
+				if ( slapi_plugins_used ) {
+					slapi_int_free_object_extensions( SLAPI_X_EXT_CONNECTION,
+						&conn[j] );
+				}
+#endif
+			}
+		}
+	}
+
+	for ( i = 0; i < NUM_CONNECTION_ARRAY; i++ ) {
+		free( connections[i] );
+		connections[i] = NULL;
+		ldap_pvt_thread_mutex_destroy( &connections_mutex[i] );
+	}
+
+	free( connections );
+	free( connections_mutex );
+
+	ldap_pvt_thread_mutex_destroy( &conn_nextid_mutex );
+
+	return 0;
+
+}
+#else
 {
 	ber_socket_t i;
 
@@ -187,14 +317,50 @@ int connections_destroy(void)
 	ldap_pvt_thread_mutex_destroy( &conn_nextid_mutex );
 	return 0;
 }
+#endif
 
 /*
  * shutdown all connections
  */
 int connections_shutdown(void)
+#ifdef SLAP_MULTI_CONN_ARRAY
+{
+	int i;
+	ber_socket_t j;
+
+	for ( i = 0; i < NUM_CONNECTION_ARRAY; i++ ) {
+		Connection* conn = connections[i];
+		ldap_pvt_thread_mutex_lock( &connections_mutex[i] );
+		for ( j = 0; j < MCA_ARRAY_SIZE; j++ ) {
+			if( conn[j].c_struct_state != SLAP_C_USED ) {
+				continue;
+			}
+			/* give persistent clients a chance to cleanup */
+			if( conn[j].c_conn_state == SLAP_C_CLIENT ) {
+				ldap_pvt_thread_pool_submit( &connection_pool,
+				conn[j].c_clientfunc, conn[j].c_clientarg );
+				continue;
+			}
+
+			ldap_pvt_thread_mutex_lock( &conn[j].c_mutex );
+			/* connections_mutex and c_mutex are locked */
+			connection_closing( &conn[j], "connection shutdown" );
+			connection_close( &conn[j] );
+			ldap_pvt_thread_mutex_unlock( &conn[j].c_mutex );
+		}
+
+		ldap_pvt_thread_mutex_unlock( &connections_mutex[i] );
+	}
+
+	return 0;
+
+}
+#else
 {
 	ber_socket_t i;
 
+	ldap_pvt_thread_mutex_lock( &connections_mutex );
+
 	for ( i = 0; i < dtblsize; i++ ) {
 		if( connections[i].c_struct_state != SLAP_C_USED ) {
 			continue;
@@ -208,15 +374,18 @@ int connections_shutdown(void)
 
 		ldap_pvt_thread_mutex_lock( &connections[i].c_mutex );
 
-		/* c_mutex is locked */
+		/* connections_mutex and c_mutex are locked */
 		connection_closing( &connections[i], "slapd shutdown" );
 		connection_close( &connections[i] );
 
 		ldap_pvt_thread_mutex_unlock( &connections[i].c_mutex );
 	}
 
+	ldap_pvt_thread_mutex_unlock( &connections_mutex );
+
 	return 0;
 }
+#endif
 
 /*
  * Timeout idle connections.
@@ -251,6 +420,8 @@ int connections_timeout_idle(time_t now)
 
 static Connection* connection_get( ber_socket_t s )
 {
+	/* connections_mutex should be locked by caller */
+
 	Connection *c;
 
 	Debug( LDAP_DEBUG_ARGS,
@@ -262,19 +433,15 @@ static Connection* connection_get( ber_socket_t s )
 	if(s == AC_SOCKET_INVALID) return NULL;
 
 #ifndef HAVE_WINSOCK
-	assert( s < dtblsize );
+	assert( MCA_conn_check( s ) );
-	c = &connections[s];
+	c = MCA_GET_CONNECTION(s);
 
 #else
 	c = NULL;
 	{
 		ber_socket_t i, sd;
 
-		ldap_pvt_thread_mutex_lock( &connections_mutex );
 		for(i=0; i<dtblsize; i++) {
-			if( connections[i].c_struct_state == SLAP_C_PENDING )
-				continue;
-
 			if( connections[i].c_struct_state == SLAP_C_UNINITIALIZED ) {
 				assert( connections[i].c_conn_state == SLAP_C_INVALID );
 				assert( connections[i].c_sb == 0 );
@@ -299,7 +466,6 @@ static Connection* connection_get( ber_socket_t s )
 				break;
 			}
 		}
-		ldap_pvt_thread_mutex_unlock( &connections_mutex );
 	}
 #endif
 
@@ -362,7 +528,6 @@ long connection_init(
 {
 	unsigned long id;
 	Connection *c;
-	int doinit = 0;
 
 	assert( connections != NULL );
 
@@ -383,29 +548,24 @@ long connection_init(
 	assert( s >= 0 );
 #ifndef HAVE_WINSOCK
 	assert( s < dtblsize );
-	c = &connections[s];
+#endif
-	if( c->c_struct_state == SLAP_C_UNINITIALIZED ) {
+
-		doinit = 1;
+	ldap_pvt_thread_mutex_lock( MCA_GET_CONN_MUTEX(s) );
-	} else {
+
-		assert( c->c_struct_state == SLAP_C_UNUSED );
+#ifndef HAVE_WINSOCK
-	}
+	assert( MCA_conn_check( s ) );
+	c = MCA_GET_CONNECTION(s);
 #else
 	{
 		ber_socket_t i;
 		c = NULL;
 
-		ldap_pvt_thread_mutex_lock( &connections_mutex );
 		for( i=0; i < dtblsize; i++) {
 			ber_socket_t	sd;
 
-			if ( connections[i].c_struct_state == SLAP_C_PENDING )
-				continue;
-
 			if( connections[i].c_struct_state == SLAP_C_UNINITIALIZED ) {
 				assert( connections[i].c_sb == 0 );
 				c = &connections[i];
-				c->c_struct_state = SLAP_C_PENDING;
-				doinit = 1;
 				break;
 			}
 
@@ -418,7 +578,6 @@ long connection_init(
 			if( connections[i].c_struct_state == SLAP_C_UNUSED ) {
 				assert( sd == AC_SOCKET_INVALID );
 				c = &connections[i];
-				c->c_struct_state = SLAP_C_PENDING;
 				break;
 			}
 
@@ -428,18 +587,20 @@ long connection_init(
 			assert( connections[i].c_conn_state != SLAP_C_INVALID );
 			assert( sd != AC_SOCKET_INVALID );
 		}
-		ldap_pvt_thread_mutex_unlock( &connections_mutex );
 
 		if( c == NULL ) {
 			Debug( LDAP_DEBUG_ANY,
 				"connection_init(%d): connection table full "
 				"(%d/%d)\n", s, i, dtblsize);
+			ldap_pvt_thread_mutex_unlock( &connections_mutex );
 			return -1;
 		}
 	}
 #endif
 
-	if( doinit ) {
+	assert( c != NULL );
+
+	if( c->c_struct_state == SLAP_C_UNINITIALIZED ) {
 		c->c_send_ldap_result = slap_send_ldap_result;
 		c->c_send_search_entry = slap_send_search_entry;
 		c->c_send_search_reference = slap_send_search_reference;
@@ -489,10 +650,13 @@ long connection_init(
 			slapi_int_create_object_extensions( SLAPI_X_EXT_CONNECTION, c );
 		}
 #endif
+
+		c->c_struct_state = SLAP_C_UNUSED;
 	}
 
 	ldap_pvt_thread_mutex_lock( &c->c_mutex );
 
+	assert( c->c_struct_state == SLAP_C_UNUSED );
 	assert( BER_BVISNULL( &c->c_authmech ) );
 	assert( BER_BVISNULL( &c->c_dn ) );
 	assert( BER_BVISNULL( &c->c_ndn ) );
@@ -523,6 +687,7 @@ long connection_init(
 		c->c_close_reason = "?";			/* should never be needed */
 		ber_sockbuf_ctrl( c->c_sb, LBER_SB_OPT_SET_FD, &s );
 		ldap_pvt_thread_mutex_unlock( &c->c_mutex );
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 
 		return 0;
 	}
@@ -611,6 +776,7 @@ long connection_init(
 
 	slapd_add_internal( s, 1 );
 	ldap_pvt_thread_mutex_unlock( &c->c_mutex );
+	ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 
 	backend_connection_init(c);
 
@@ -653,6 +819,7 @@ void connection2anonymous( Connection *c )
 static void
 connection_destroy( Connection *c )
 {
+	/* note: connections_mutex should be locked by caller */
 	ber_socket_t	sd;
 	unsigned long	connid;
 	const char		*close_reason;
@@ -674,10 +841,6 @@ connection_destroy( Connection *c )
 	connid = c->c_connid;
 	close_reason = c->c_close_reason;
 
-	ldap_pvt_thread_mutex_lock( &connections_mutex );
-	c->c_struct_state = SLAP_C_PENDING;
-	ldap_pvt_thread_mutex_unlock( &connections_mutex );
-
 	backend_connection_destroy(c);
 
 	c->c_protocol = 0;
@@ -850,7 +1013,7 @@ static void connection_close( Connection *c )
 	assert( c->c_struct_state == SLAP_C_USED );
 	assert( c->c_conn_state == SLAP_C_CLOSING );
 
-	/* note: c_mutex should be locked by caller */
+	/* note: connections_mutex and c_mutex should be locked by caller */
 
 	ber_sockbuf_ctrl( c->c_sb, LBER_SB_OPT_GET_FD, &sd );
 	if( !LDAP_STAILQ_EMPTY(&c->c_ops) ) {
@@ -881,21 +1044,71 @@ unsigned long connections_nextid(void)
 
 Connection* connection_first( ber_socket_t *index )
 {
+#ifdef SLAP_MULTI_CONN_ARRAY
+	int conn_array_id;
+#endif
+
 	assert( connections != NULL );
 	assert( index != NULL );
 
-	ldap_pvt_thread_mutex_lock( &connections_mutex );
+#ifdef SLAP_MULTI_CONN_ARRAY
-	for( *index = 0; *index < dtblsize; (*index)++) {
+	for ( conn_array_id = 0;
-		if( connections[*index].c_struct_state != SLAP_C_UNINITIALIZED ) {
+		conn_array_id < NUM_CONNECTION_ARRAY;
-			break;
+		conn_array_id++ )
-		}
+	{
+		ldap_pvt_thread_mutex_lock( &connections_mutex[ conn_array_id ] );
 	}
-	ldap_pvt_thread_mutex_unlock( &connections_mutex );
+#else
+	ldap_pvt_thread_mutex_lock( &connections_mutex );
+#endif
+
+	*index = 0;
 
 	return connection_next(NULL, index);
 }
 
 Connection* connection_next( Connection *c, ber_socket_t *index )
+#ifdef SLAP_MULTI_CONN_ARRAY
+{
+	Connection* conn;
+
+	assert( connections != NULL );
+	assert( index != NULL );
+	assert( *index >= 0 && *index <= dtblsize );
+
+	if( c != NULL ) ldap_pvt_thread_mutex_unlock( &c->c_mutex );
+
+	c = NULL;
+
+	for(; *index < dtblsize; (*index)++) {
+		assert( MCA_conn_check( *index ) );
+		conn = MCA_GET_CONNECTION(*index);
+		if( conn->c_struct_state == SLAP_C_UNINITIALIZED ) {
+			assert( conn->c_conn_state == SLAP_C_INVALID );
+#ifndef HAVE_WINSOCK
+			continue;
+#else
+			break;
+#endif
+		}
+
+		if( conn->c_struct_state == SLAP_C_USED ) {
+			assert( conn->c_conn_state != SLAP_C_INVALID );
+			c = conn;
+			(*index)++;
+			break;
+		}
+
+		assert( conn->c_struct_state == SLAP_C_UNUSED );
+		assert( conn->c_conn_state == SLAP_C_INVALID );
+	}
+
+	if( c != NULL ) ldap_pvt_thread_mutex_lock( &c->c_mutex );
+
+	return c;
+
+}
+#else
 {
 	assert( connections != NULL );
 	assert( index != NULL );
@@ -905,11 +1118,14 @@ Connection* connection_next( Connection *c, ber_socket_t *index )
 
 	c = NULL;
 
-	ldap_pvt_thread_mutex_lock( &connections_mutex );
 	for(; *index < dtblsize; (*index)++) {
 		if( connections[*index].c_struct_state == SLAP_C_UNINITIALIZED ) {
 			assert( connections[*index].c_conn_state == SLAP_C_INVALID );
+#ifndef HAVE_WINSOCK
+			continue;
+#else
 			break;
+#endif
 		}
 
 		if( connections[*index].c_struct_state == SLAP_C_USED ) {
@@ -923,15 +1139,30 @@ Connection* connection_next( Connection *c, ber_socket_t *index )
 	}
 
 	if( c != NULL ) ldap_pvt_thread_mutex_lock( &c->c_mutex );
-	ldap_pvt_thread_mutex_unlock( &connections_mutex );
 	return c;
 }
+#endif
 
 void connection_done( Connection *c )
 {
+#ifdef SLAP_MULTI_CONN_ARRAY
+	int conn_array_id;
+#endif
+
 	assert( connections != NULL );
 
 	if( c != NULL ) ldap_pvt_thread_mutex_unlock( &c->c_mutex );
+
+#ifdef SLAP_MULTI_CONN_ARRAY
+	for ( conn_array_id = 0;
+		conn_array_id < NUM_CONNECTION_ARRAY;
+		conn_array_id++ )
+	{
+		ldap_pvt_thread_mutex_unlock( &connections_mutex[ conn_array_id ] );
+	}
+#else
+	ldap_pvt_thread_mutex_unlock( &connections_mutex );
+#endif
 }
 
 /*
@@ -1293,6 +1524,8 @@ int connection_read(ber_socket_t s)
 
 	assert( connections != NULL );
 
+	ldap_pvt_thread_mutex_lock( MCA_GET_CONN_MUTEX(s) );
+
 	/* get (locked) connection */
 	c = connection_get( s );
 
@@ -1301,6 +1534,7 @@ int connection_read(ber_socket_t s)
 			"connection_read(%ld): no connection!\n",
 			(long) s, 0, 0 );
 
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 		return -1;
 	}
 
@@ -1315,6 +1549,7 @@ int connection_read(ber_socket_t s)
 		slapd_set_read( s, 1 );
 #endif
 		connection_return( c );
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 		return 0;
 	}
 
@@ -1329,6 +1564,7 @@ int connection_read(ber_socket_t s)
 			c->c_clientfunc, c->c_clientarg );
 #endif
 		connection_return( c );
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 		return 0;
 	}
 
@@ -1346,7 +1582,7 @@ int connection_read(ber_socket_t s)
 				s, rc, c->c_connid );
 
 			c->c_needs_tls_accept = 0;
-			/* c_mutex is locked */
+			/* connections_mutex and c_mutex are locked */
 			connection_closing( c, "TLS negotiation failure" );
 
 #if 0
@@ -1370,6 +1606,7 @@ int connection_read(ber_socket_t s)
 
 			connection_close( c );
 			connection_return( c );
+			ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 			return 0;
 
 		} else if ( rc == 0 ) {
@@ -1408,6 +1645,7 @@ int connection_read(ber_socket_t s)
 #endif
 
 			connection_return( c );
+			ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 			return 0;
 		}
 	}
@@ -1422,6 +1660,7 @@ int connection_read(ber_socket_t s)
 #endif
 
 			connection_return( c );
+			ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 			return 0;
 		}
 
@@ -1434,10 +1673,11 @@ int connection_read(ber_socket_t s)
 				"error=%d id=%lu, closing\n",
 				s, rc, c->c_connid );
 
-			/* c_mutex is locked */
+			/* connections_mutex and c_mutex are locked */
 			connection_closing( c, "SASL layer install failure" );
 			connection_close( c );
 			connection_return( c );
+			ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 			return 0;
 		}
 	}
@@ -1467,10 +1707,11 @@ int connection_read(ber_socket_t s)
 			"connection_read(%d): input error=%d id=%lu, closing.\n",
 			s, rc, c->c_connid );
 
-		/* c_mutex is locked */
+		/* connections_mutex and c_mutex are locked */
 		connection_closing( c, conn_lost_str );
 		connection_close( c );
 		connection_return( c );
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 		return 0;
 	}
 
@@ -1491,6 +1732,7 @@ int connection_read(ber_socket_t s)
 #endif
 
 	connection_return( c );
+	ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 
 	return 0;
 }
@@ -1731,6 +1973,23 @@ connection_resched( Connection *conn )
 		ber_socket_t	sd;
 		ber_sockbuf_ctrl( conn->c_sb, LBER_SB_OPT_GET_FD, &sd );
 
+		/* use trylock to avoid possible deadlock */
+		rc = ldap_pvt_thread_mutex_trylock( MCA_GET_CONN_MUTEX( sd ) );
+
+		if( rc ) {
+			Debug( LDAP_DEBUG_TRACE,
+				"connection_resched: reaquiring locks conn=%lu sd=%d\n",
+				conn->c_connid, sd, 0 );
+			/*
+			 * reaquire locks in the right order...
+			 * this may allow another thread to close this connection,
+			 * so recheck state below.
+			 */
+			ldap_pvt_thread_mutex_unlock( &conn->c_mutex );
+			ldap_pvt_thread_mutex_lock( MCA_GET_CONN_MUTEX ( sd ) );
+			ldap_pvt_thread_mutex_lock( &conn->c_mutex );
+		}
+
 		if( conn->c_conn_state != SLAP_C_CLOSING ) {
 			Debug( LDAP_DEBUG_TRACE, "connection_resched: "
 				"closed by other thread conn=%lu sd=%d\n",
@@ -1742,6 +2001,7 @@ connection_resched( Connection *conn )
 			connection_close( conn );
 		}
 
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX( sd ) );
 		return 0;
 	}
 
@@ -1921,11 +2181,14 @@ int connection_write(ber_socket_t s)
 
 	slapd_clr_write( s, 0 );
 
+	ldap_pvt_thread_mutex_lock( MCA_GET_CONN_MUTEX( s ) );
+
 	c = connection_get( s );
 	if( c == NULL ) {
 		Debug( LDAP_DEBUG_ANY,
 			"connection_write(%ld): no connection!\n",
 			(long)s, 0, 0 );
+		ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX( s ) );
 		return -1;
 	}
 
@@ -1965,6 +2228,7 @@ int connection_write(ber_socket_t s)
 	}
 
 	connection_return( c );
+	ldap_pvt_thread_mutex_unlock( MCA_GET_CONN_MUTEX(s) );
 	return 0;
 }