NFS: Clean up nfs_sb_active/nfs_sb_deactive

Instead of causing umount requests to block on server->active_wq while the
asynchronous sillyrename deletes are executing, we can use the sb->s_active
counter to obtain a reference to the super_block, and then release that
reference in nfs_async_unlink_release().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index e9b2017..e527fab 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -209,7 +209,6 @@
 static int nfs_xdev_get_sb(struct file_system_type *fs_type,
 		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
 static void nfs_kill_super(struct super_block *);
-static void nfs_put_super(struct super_block *);
 static int nfs_remount(struct super_block *sb, int *flags, char *raw_data);
 
 static struct file_system_type nfs_fs_type = {
@@ -232,7 +231,6 @@
 	.alloc_inode	= nfs_alloc_inode,
 	.destroy_inode	= nfs_destroy_inode,
 	.write_inode	= nfs_write_inode,
-	.put_super	= nfs_put_super,
 	.statfs		= nfs_statfs,
 	.clear_inode	= nfs_clear_inode,
 	.umount_begin	= nfs_umount_begin,
@@ -337,26 +335,20 @@
 	unregister_filesystem(&nfs_fs_type);
 }
 
-void nfs_sb_active(struct nfs_server *server)
-{
-	atomic_inc(&server->active);
-}
-
-void nfs_sb_deactive(struct nfs_server *server)
-{
-	if (atomic_dec_and_test(&server->active))
-		wake_up(&server->active_wq);
-}
-
-static void nfs_put_super(struct super_block *sb)
+void nfs_sb_active(struct super_block *sb)
 {
 	struct nfs_server *server = NFS_SB(sb);
-	/*
-	 * Make sure there are no outstanding ops to this server.
-	 * If so, wait for them to finish before allowing the
-	 * unmount to continue.
-	 */
-	wait_event(server->active_wq, atomic_read(&server->active) == 0);
+
+	if (atomic_inc_return(&server->active) == 1)
+		atomic_inc(&sb->s_active);
+}
+
+void nfs_sb_deactive(struct super_block *sb)
+{
+	struct nfs_server *server = NFS_SB(sb);
+
+	if (atomic_dec_and_test(&server->active))
+		deactivate_super(sb);
 }
 
 /*