From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753815Ab2GQArr (ORCPT ); Mon, 16 Jul 2012 20:47:47 -0400 Received: from smtp-01.mandic.com.br ([200.225.81.132]:34018 "EHLO smtp-01.mandic.com.br" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180Ab2GQAro (ORCPT ); Mon, 16 Jul 2012 20:47:44 -0400 X-Greylist: delayed 398 seconds by postgrey-1.27 at vger.kernel.org; Mon, 16 Jul 2012 20:47:44 EDT Message-ID: <5004B49C.6010708@cesarb.net> Date: Mon, 16 Jul 2012 21:41:00 -0300 From: Cesar Eduardo Barros User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: linux-kernel@vger.kernel.org, Dan Magenheimer , linux-mm@kvack.org Subject: Re: frontswap: is frontswap_init called from swapoff safe? References: <4FCDE270.1020906@cesarb.net> <20120607003720.GI9472@phenom.dumpdata.com> In-Reply-To: <20120607003720.GI9472@phenom.dumpdata.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em 06-06-2012 21:37, Konrad Rzeszutek Wilk escreveu: > On Tue, Jun 05, 2012 at 07:41:52AM -0300, Cesar Eduardo Barros wrote: >> 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. > > Let me look at this - can't do it this week - but will get back to you > shortly. Did you look at it already? (Just pinging in case you forgot.) >> >> (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