[PATCH] Fix unserialized task->files changing

Fixed race on put_files_struct on exec with proc.  Restoring files on
current on error path may lead to proc having a pointer to already kfree-d
files_struct.

->files changing at exit.c and khtread.c are safe as exit_files() makes all
things under lock.

Found during OpenVZ stress testing.

[akpm@osdl.org: add export]
Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/binfmt_elf.c

@@ -1038,10 +1038,8 @@ out_free_interp:
 out_free_file:
 	sys_close(elf_exec_fileno);
 out_free_fh:
-	if (files) {
-		put_files_struct(current->files);
-		current->files = files;
-	}
+	if (files)
+		reset_files_struct(current, files);
 out_free_ph:
 	kfree(elf_phdata);
 	goto out;