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.

sys/kern/kern_descrip.c

@@ -2070,13 +2070,11 @@ fdrop_locked(fp, td)
 	FILE_UNLOCK(fp);
 	if (fp->f_count < 0)
 		panic("fdrop: count < 0");
-	mtx_lock(&Giant);
 	if (fp->f_ops != &badfileops)
 		error = fo_close(fp, td);
 	else
 		error = 0;
 	ffree(fp);
-	mtx_unlock(&Giant);
 	return (error);
 }
 

sys/kern/kern_event.c

@@ -906,7 +906,7 @@ kqueue_close(struct file *fp, struct thread *td)
 	struct knote **knp, *kn, *kn0;
 	int i;
 
-	GIANT_REQUIRED;
+	mtx_lock(&Giant);
 
 	FILEDESC_LOCK(fdp);
 	for (i = 0; i < fdp->fd_knlistsize; i++) {
@@ -957,6 +957,7 @@ kqueue_close(struct file *fp, struct thread *td)
 	free(kq, M_KQUEUE);
 	fp->f_data = NULL;
 
+	mtx_unlock(&Giant);
 	return (0);
 }
 

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);
 }

sys/kern/vfs_vnops.c

@@ -915,11 +915,11 @@ vn_closefile(fp, td)
 {
 	struct vnode *vp;
 	struct flock lf;
-
-	GIANT_REQUIRED;
+	int error;
 
 	vp = fp->f_vnode;
 
+	mtx_lock(&Giant);
 	if (fp->f_type == DTYPE_VNODE && fp->f_flag & FHASLOCK) {
 		lf.l_whence = SEEK_SET;
 		lf.l_start = 0;
@@ -930,7 +930,9 @@ vn_closefile(fp, td)
 
 	fp->f_ops = &badfileops;
 
-	return (vn_close(vp, fp->f_flag, fp->f_cred, td));
+	error = vn_close(vp, fp->f_flag, fp->f_cred, td);
+	mtx_unlock(&Giant);
+	return (error);
 }
 
 /*

sys/opencrypto/cryptodev.c

@@ -623,12 +623,19 @@ cryptof_close(struct file *fp, struct thread *td)
 	struct fcrypt *fcr = fp->f_data;
 	struct csession *cse;
 
+	/*
+	 * XXXRW: The cryptodev and called code all appears to be
+	 * MPSAFE, but I'm not set up to test it.  Acquire Giant
+	 * for now.
+	 */
+	mtx_lock(&Giant);
 	while ((cse = TAILQ_FIRST(&fcr->csessions))) {
 		TAILQ_REMOVE(&fcr->csessions, cse, next);
 		(void)csefree(cse);
 	}
 	FREE(fcr, M_XDATA);
 	fp->f_data = NULL;
+	mtx_unlock(&Giant);
 	return 0;
 }