don't bother with call_rcu() in put_files_struct()

At that point nobody can see us anyway; everything that
looks at files_fdtable(files) is separated from the
guts of put_files_struct(files) - either since files is
current->files or because we fetched it under task_lock()
and hadn't dropped that yet, or because we'd bumped
files->count while holding task_lock()...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/file.c

@@ -447,18 +447,14 @@ void put_files_struct(struct files_struct *files)
 
 	if (atomic_dec_and_test(&files->count)) {
 		close_files(files);
-		/*
-		 * Free the fd and fdset arrays if we expanded them.
-		 * If the fdtable was embedded, pass files for freeing
-		 * at the end of the RCU grace period. Otherwise,
-		 * you can free files immediately.
-		 */
+		/* not really needed, since nobody can see us */
 		rcu_read_lock();
 		fdt = files_fdtable(files);
+		rcu_read_unlock();
+		/* free the arrays if they are not embedded */
 		if (fdt != &files->fdtab)
+			__free_fdtable(fdt);
 		kmem_cache_free(files_cachep, files);
-		free_fdtable(fdt);
-		rcu_read_unlock();
 	}
 }