From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it. Date: Fri, 7 Jun 2013 12:29:15 -0700 (PDT) Message-ID: <1370633355-21201-1-git-send-email-konrad.wilk@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ascii Content-Transfer-Encoding: 7bit Return-path: Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com Cc: dan.magenheimer@oracle.com, Konrad Rzeszutek Wilk List-Id: xen-devel@lists.xenproject.org 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