[readdir] convert ext3

new helper: dir_relax(inode).  Call when you are in location that will
_not_ be invalidated by directory modifications (block boundary, in case
of ext*).  Returns whether the directory has survived (dropping i_mutex
allows rmdir to kill the sucker; if it returns false to us, ->iterate()
is obviously done)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 40293a6..aa9770c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2725,5 +2725,11 @@
 	}
 	return true;
 }
+static inline bool dir_relax(struct inode *inode)
+{
+	mutex_unlock(&inode->i_mutex);
+	mutex_lock(&inode->i_mutex);
+	return !IS_DEADDIR(inode);
+}
 
 #endif /* _LINUX_FS_H */