hfsplus: switch to ->iterate_shared()

We need to protect the list of hfsplus_readdir_data against parallel
insertions (in readdir) and removals (in release).  Add a spinlock
for that.  Note that it has nothing to do with protection of
hfsplus_readdir_data->key - we have an exclusion between hfsplus_readdir()
and hfsplus_delete_cat() on directory lock and between several
hfsplus_readdir() for the same struct file on ->f_pos_lock.  The spinlock
is strictly for list changes.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/hfsplus/inode.c

@@ -374,6 +374,7 @@ struct inode *hfsplus_new_inode(struct super_block *sb, umode_t mode)
 
 	hip = HFSPLUS_I(inode);
 	INIT_LIST_HEAD(&hip->open_dir_list);
+	spin_lock_init(&hip->open_dir_lock);
 	mutex_init(&hip->extents_lock);
 	atomic_set(&hip->opencnt, 0);
 	hip->extent_state = 0;