Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757213Ab3FHBHZ (ORCPT ); Fri, 7 Jun 2013 21:07:25 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:45160 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756445Ab3FHBHY (ORCPT ); Fri, 7 Jun 2013 21:07:24 -0400 Message-ID: <51B283C4.4070803@oracle.com> Date: Sat, 08 Jun 2013 09:07:16 +0800 From: Bob Liu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, dan.magenheimer@oracle.com Subject: Re: [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it. References: <1370633355-21201-1-git-send-email-konrad.wilk@oracle.com> <20130607194534.GB21543@phenom.dumpdata.com> In-Reply-To: <20130607194534.GB21543@phenom.dumpdata.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2575 Lines: 72 On 06/08/2013 03:45 AM, Konrad Rzeszutek Wilk wrote: > 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 Nice catch! Reviewed-by: Bob Liu >> --- >> 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 >> -- Regards, -Bob -- 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/