From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 124226B0062 for ; Wed, 6 Jun 2012 20:44:25 -0400 (EDT) Date: Wed, 6 Jun 2012 20:37:20 -0400 From: Konrad Rzeszutek Wilk Subject: Re: frontswap: is frontswap_init called from swapoff safe? Message-ID: <20120607003720.GI9472@phenom.dumpdata.com> References: <4FCDE270.1020906@cesarb.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FCDE270.1020906@cesarb.net> Sender: owner-linux-mm@kvack.org List-ID: To: Cesar Eduardo Barros Cc: linux-kernel@vger.kernel.org, Dan Magenheimer , linux-mm@kvack.org 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. > > (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