From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx147.postini.com [74.125.245.147]) by kanga.kvack.org (Postfix) with SMTP id 4AF256B0062 for ; Tue, 5 Jun 2012 06:41:56 -0400 (EDT) Message-ID: <4FCDE270.1020906@cesarb.net> Date: Tue, 05 Jun 2012 07:41:52 -0300 From: Cesar Eduardo Barros MIME-Version: 1.0 Subject: frontswap: is frontswap_init called from swapoff safe? Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: Konrad Rzeszutek Wilk , Dan Magenheimer , linux-mm@kvack.org I was looking at the swapfile.c parts of the recently-merged frontswap, and noticed that frontswap_init can be called from swapoff when try_to_unuse fails. This looks odd to me. Whether it is safe or not depends on what frontswap_ops.init does, but the comment for __frontswap_init ("Called when a swap device is swapon'd") and the function name itself seem to imply it should be called only for swapon, not when relinking the swap_info after a failed swapoff. In particular, if frontswap_ops.init assumes the swap map is empty, it would break, since as far as I know when try_to_unuse fails there are still pages in the swap. (By the way, the comment above enable_swap_info at sys_swapoff needs to be updated to also explain why reading p->frontswap_map outside the lock is safe at that point, like it does for p->prio and p->swap_map.) -- Cesar Eduardo Barros cesarb@cesarb.net cesar.barros@gmail.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org