NFS: Stop sillyname renames and unmounts from racing

Added an active/deactive mechanism to the nfs_server structure
allowing async operations to hold off umount until the
operations are done.

Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_fs_sb.h

@@ -3,6 +3,9 @@
 
 #include <linux/list.h>
 #include <linux/backing-dev.h>
+#include <linux/wait.h>
+
+#include <asm/atomic.h>
 
 struct nfs_iostats;
 
@@ -110,6 +113,9 @@ struct nfs_server {
 						   filesystem */
 #endif
 	void (*destroy)(struct nfs_server *);
+
+	atomic_t active; /* Keep trace of any activity to this server */
+	wait_queue_head_t active_wq;  /* Wait for any activity to stop  */
 };
 
 /* Server capabilities */