Push acquisition of Giant from fdrop_closed() into fo_close() so that

individual file object implementations can optionally acquire Giant if
they require it:

- soo_close(): depends on debug.mpsafenet
- pipe_close(): Giant not acquired
- kqueue_close(): Giant required
- vn_close(): Giant required
- cryptof_close(): Giant required (conservative)

Notes:

  Giant is still acquired in close() even when closing MPSAFE objects
  due to kqueue requiring Giant in the calling closef() code.
  Microbenchmarks indicate that this removal of Giant cuts 3%-3% off
  of pipe create/destroy pairs from user space with SMP compiled into
  the kernel.

  The cryptodev and opencrypto code appears MPSAFE, but I'm unable to
  test it extensively and so have left Giant over fo_close().  It can
  probably be removed given some testing and review.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/kern/sys_socket.c b/sys/kern/sys_socket.c
index e59823c..e1de4b7 100644
--- a/sys/kern/sys_socket.c
+++ b/sys/kern/sys_socket.c
@@ -262,11 +262,13 @@ soo_close(fp, td)
 	int error = 0;
 	struct socket *so;
 
+	NET_LOCK_GIANT();
 	so = fp->f_data;
 	fp->f_ops = &badfileops;
 	fp->f_data = NULL;
 
 	if (so)
 		error = soclose(so);
+	NET_UNLOCK_GIANT();
 	return (error);
 }