From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7A1BC43603 for ; Tue, 17 Dec 2019 16:13:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B40F024679 for ; Tue, 17 Dec 2019 16:13:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727822AbfLQQNs (ORCPT ); Tue, 17 Dec 2019 11:13:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:48522 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726858AbfLQQNr (ORCPT ); Tue, 17 Dec 2019 11:13:47 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 5DB33AB7F; Tue, 17 Dec 2019 16:13:45 +0000 (UTC) Subject: Re: [PATCH v11 2/6] xenbus/backend: Protect xenbus callback with lock To: SeongJae Park , axboe@kernel.dk, konrad.wilk@oracle.com, roger.pau@citrix.com Cc: SeongJae Park , pdurrant@amazon.com, sj38.park@gmail.com, xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20191217160748.693-1-sjpark@amazon.com> <20191217160748.693-3-sjpark@amazon.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <44327bf3-45ed-3e5a-3984-36ea40f53fc5@suse.com> Date: Tue, 17 Dec 2019 17:13:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: <20191217160748.693-3-sjpark@amazon.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 17.12.19 17:07, SeongJae Park wrote: > From: SeongJae Park > > 'reclaim_memory' callback can race with a driver code as this callback > will be called from any memory pressure detected context. To deal with > the case, this commit adds a spinlock in the 'xenbus_device'. Whenever > 'reclaim_memory' callback is called, the lock of the device which passed > to the callback as its argument is locked. Thus, drivers registering > their 'reclaim_memory' callback should protect the data that might race > with the callback with the lock by themselves. > > Signed-off-by: SeongJae Park > --- > drivers/xen/xenbus/xenbus_probe.c | 1 + > drivers/xen/xenbus/xenbus_probe_backend.c | 10 ++++++++-- > include/xen/xenbus.h | 2 ++ > 3 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c > index 5b471889d723..b86393f172e6 100644 > --- a/drivers/xen/xenbus/xenbus_probe.c > +++ b/drivers/xen/xenbus/xenbus_probe.c > @@ -472,6 +472,7 @@ int xenbus_probe_node(struct xen_bus_type *bus, > goto fail; > > dev_set_name(&xendev->dev, "%s", devname); > + spin_lock_init(&xendev->reclaim_lock); > > /* Register with generic device framework. */ > err = device_register(&xendev->dev); > diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c > index 7e78ebef7c54..516aa64b9967 100644 > --- a/drivers/xen/xenbus/xenbus_probe_backend.c > +++ b/drivers/xen/xenbus/xenbus_probe_backend.c > @@ -251,12 +251,18 @@ static int backend_probe_and_watch(struct notifier_block *notifier, > static int backend_reclaim_memory(struct device *dev, void *data) > { > const struct xenbus_driver *drv; > + struct xenbus_device *xdev; > + unsigned long flags; > > if (!dev->driver) > return 0; > drv = to_xenbus_driver(dev->driver); > - if (drv && drv->reclaim_memory) > - drv->reclaim_memory(to_xenbus_device(dev)); > + if (drv && drv->reclaim_memory) { > + xdev = to_xenbus_device(dev); > + spin_trylock_irqsave(&xdev->reclaim_lock, flags); You need spin_lock_irqsave() here. Or maybe spin_lock() would be fine, too? I can't see a reason why you'd want to disable irqs here. > + drv->reclaim_memory(xdev); > + spin_unlock_irqrestore(&xdev->reclaim_lock, flags); > + } > return 0; > } > > diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h > index c861cfb6f720..d9468313061d 100644 > --- a/include/xen/xenbus.h > +++ b/include/xen/xenbus.h > @@ -76,6 +76,8 @@ struct xenbus_device { > enum xenbus_state state; > struct completion down; > struct work_struct work; > + /* 'reclaim_memory' callback is called while this lock is acquired */ > + spinlock_t reclaim_lock; > }; > > static inline struct xenbus_device *to_xenbus_device(struct device *dev) > Juergen