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, 4 insertions, 7 deletions

diff --git a/sys/netinet/accf_data.c b/sys/netinet/accf_data.c
index 1bbd3fe..599392c 100644
--- a/sys/netinet/accf_data.c
+++ b/sys/netinet/accf_data.c
@@ -38,7 +38,7 @@ __FBSDID("$FreeBSD$");
 
 /* accept filter that holds a socket until data arrives */
 
-static void	sohasdata(struct socket *so, void *arg, int waitflag);
+static int	sohasdata(struct socket *so, void *arg, int waitflag);
 
 static struct accept_filter accf_data_filter = {
 	"dataready",
@@ -55,15 +55,12 @@ static moduledata_t accf_data_mod = {
 
 DECLARE_MODULE(accf_data, accf_data_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
 
-static void
+static int
 sohasdata(struct socket *so, void *arg, int waitflag)
 {
 
 	if (!soreadable(so))
-		return;
+		return (SU_OK);
 
-	so->so_upcall = NULL;
-	so->so_rcv.sb_flags &= ~SB_UPCALL;
-	soisconnected(so);
-	return;
+	return (SU_ISCONNECTED);
 }