Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756865Ab3FGTpo (ORCPT ); Fri, 7 Jun 2013 15:45:44 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:38288 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755360Ab3FGTpn (ORCPT ); Fri, 7 Jun 2013 15:45:43 -0400 Date: Fri, 7 Jun 2013 15:45:34 -0400 From: Konrad Rzeszutek Wilk To: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, bob.liu@oracle.com Cc: dan.magenheimer@oracle.com Subject: Re: [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it. Message-ID: <20130607194534.GB21543@phenom.dumpdata.com> References: <1370633355-21201-1-git-send-email-konrad.wilk@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1370633355-21201-1-git-send-email-konrad.wilk@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2394 Lines: 63 On Fri, Jun 07, 2013 at 12:29:15PM -0700, Konrad Rzeszutek Wilk wrote: CC-ing Bob. > Commit 10a7a0771399a57a297fca9615450dbb3f88081a ("xen: tmem: enable Xen > tmem shim to be built/loaded as a module") allows the tmem module > to be loaded any time. For this work the frontswap API had to > be able to asynchronously to call tmem_frontswap_init before > or after the swap image had been set. That was added in git > commit 905cd0e1bf9ffe82d6906a01fd974ea0f70be97a > ("mm: frontswap: lazy initialization to allow tmem backends to build/run as modules"). > > Which means we could do this (The common case): > > modprobe tmem [so calls frontswap_register_ops, no ->init] > modifies tmem_frontswap_poolid = -1 > swapon /dev/xvda1 [__frontswap_init, calls -> init, tmem_frontswap_poolid is > < 0 so tmem hypercall done] > > Or the failing one: > > swapon /dev/xvda1 [calls __frontswap_init, sets the need_init bitmap] > modprobe tmem [calls frontswap_register_ops, -->init calls, finds out > tmem_frontswap_poolid is 0, does not make a hypercall. > Later in the module_init, sets tmem_frontswap_poolid=-1] > > Which meant that in the failing case we would not call the hypercall > to initialize the pool and never be able to make any frontswap > backend calls. > > Moving the frontswap_register_ops after setting the tmem_frontswap_poolid > fixes it. > > Signed-off-by: Konrad Rzeszutek Wilk > --- > drivers/xen/tmem.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c > index cc072c6..0f0493c 100644 > --- a/drivers/xen/tmem.c > +++ b/drivers/xen/tmem.c > @@ -379,10 +379,10 @@ static int xen_tmem_init(void) > #ifdef CONFIG_FRONTSWAP > if (tmem_enabled && frontswap) { > char *s = ""; > - struct frontswap_ops *old_ops = > - frontswap_register_ops(&tmem_frontswap_ops); > + struct frontswap_ops *old_ops; > > tmem_frontswap_poolid = -1; > + old_ops = frontswap_register_ops(&tmem_frontswap_ops); > if (IS_ERR(old_ops) || old_ops) { > if (IS_ERR(old_ops)) > return PTR_ERR(old_ops); > -- > 1.8.1.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/