Rework socket upcalls to close some races with setup/teardown of upcalls.

- Each socket upcall is now invoked with the appropriate socket buffer
  locked.  It is not permissible to call soisconnected() with this lock
  held; however, so socket upcalls now return an integer value.  The two
  possible values are SU_OK and SU_ISCONNECTED.  If an upcall returns
  SU_ISCONNECTED, then the soisconnected() will be invoked on the
  socket after the socket buffer lock is dropped.
- A new API is provided for setting and clearing socket upcalls.  The
  API consists of soupcall_set() and soupcall_clear().
- To simplify locking, each socket buffer now has a separate upcall.
- When a socket upcall returns SU_ISCONNECTED, the upcall is cleared from
  the receive socket buffer automatically.  Note that a SO_SND upcall
  should never return SU_ISCONNECTED.
- All this means that accept filters should now return SU_ISCONNECTED
  instead of calling soisconnected() directly.  They also no longer need
  to explicitly clear the upcall on the new socket.
- The HTTP accept filter still uses soupcall_set() to manage its internal
  state machine, but other accept filters no longer have any explicit
  knowlege of socket upcall internals aside from their return value.
- The various RPC client upcalls currently drop the socket buffer lock
  while invoking soreceive() as a temporary band-aid.  The plan for
  the future is to add a new flag to allow soreceive() to be called with
  the socket buffer locked.
- The AIO callback for socket I/O is now also invoked with the socket
  buffer locked.  Previously sowakeup() would drop the socket buffer
  lock only to call aio_swake() which immediately re-acquired the socket
  buffer lock for the duration of the function call.

Discussed with:	rwatson, rmacklem

1 files changed, 14 insertions, 3 deletions

diff --git a/sys/sys/socketvar.h b/sys/sys/socketvar.h
index 81e6b8825afd..6565930da6f7 100644
--- a/sys/sys/socketvar.h
+++ b/sys/sys/socketvar.h
@@ -55,6 +55,8 @@ struct vnet;
  */
 typedef	u_quad_t so_gen_t;
 
+struct socket;
+
 /*-
  * Locking key to struct socket:
  * (a) constant after allocation, no locking required.
@@ -104,8 +106,6 @@ struct socket {
 
 	struct sockbuf so_rcv, so_snd;
 
-	void	(*so_upcall)(struct socket *, void *, int);
-	void	*so_upcallarg;
 	struct	ucred *so_cred;		/* (a) user credentials */
 	struct	label *so_label;	/* (b) MAC label for socket */
 	struct	label *so_peerlabel;	/* (b) cached MAC label for peer */
@@ -280,7 +280,7 @@ struct xsocket {
 
 struct accept_filter {
 	char	accf_name[16];
-	void	(*accf_callback)
+	int	(*accf_callback)
 		(struct socket *so, void *arg, int waitflag);
 	void *	(*accf_create)
 		(struct socket *so, char *arg);
@@ -305,6 +305,14 @@ struct sockaddr;
 struct ucred;
 struct uio;
 
+/* 'which' values for socket upcalls. */
+#define	SO_RCV		1
+#define	SO_SND		2
+
+/* Return values for socket upcalls. */
+#define	SU_OK		0
+#define	SU_ISCONNECTED	1
+
 /*
  * From uipc_socket and friends
  */
@@ -356,6 +364,9 @@ int	sosend_generic(struct socket *so, struct sockaddr *addr,
 	    int flags, struct thread *td);
 int	soshutdown(struct socket *so, int how);
 void	sotoxsocket(struct socket *so, struct xsocket *xso);
+void	soupcall_clear(struct socket *so, int which);
+void	soupcall_set(struct socket *so, int which,
+	    int (*func)(struct socket *, void *, int), void *arg);
 void	sowakeup(struct socket *so, struct sockbuf *sb);
 int	selsocket(struct socket *so, int events, struct timeval *tv,
 	    struct thread *td);