From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752086AbdJTPHb (ORCPT ); Fri, 20 Oct 2017 11:07:31 -0400 Received: from esa2.dell-outbound.iphmx.com ([68.232.149.220]:3233 "EHLO esa2.dell-outbound.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751753AbdJTPH3 (ORCPT ); Fri, 20 Oct 2017 11:07:29 -0400 From: X-LoopCount0: from 10.166.132.189 X-IronPort-AV: E=Sophos;i="5.43,405,1503378000"; d="scan'208";a="76486464" X-DLP: DLP_GlobalPCIDSS To: , CC: , , , , , , , , , Subject: RE: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for drivers Thread-Topic: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for drivers Thread-Index: AQHTSbRv3hAQO0pxxkGcQBA59dRjCqLs1awg Date: Fri, 20 Oct 2017 15:07:27 +0000 Message-ID: References: <175838453318108ae69be344c4d3a2b75c2edc69.1508434514.git.mario.limonciello@dell.com> <20171020132138.GA23973@kroah.com> <19e30ca305e449de86b702ae8900d306@ausx13mpc120.AMER.DELL.COM> <20171020144839.GA4550@lst.de> In-Reply-To: <20171020144839.GA4550@lst.de> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.143.18.86] Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v9KF7ZXb015930 > -----Original Message----- > From: Christoph Hellwig [mailto:hch@lst.de] > Sent: Friday, October 20, 2017 9:49 AM > To: Limonciello, Mario > Cc: greg@kroah.com; dvhart@infradead.org; andy.shevchenko@gmail.com; linux- > kernel@vger.kernel.org; platform-driver-x86@vger.kernel.org; luto@kernel.org; > quasisec@google.com; pali.rohar@gmail.com; rjw@rjwysocki.net; > mjg59@google.com; hch@lst.de; gnomes@lxorguk.ukuu.org.uk > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for > drivers > > On Fri, Oct 20, 2017 at 01:54:36PM +0000, Mario.Limonciello@dell.com wrote: > > > -----Original Message----- > > > From: Greg KH [mailto:greg@kroah.com] > > > Sent: Friday, October 20, 2017 8:22 AM > > > To: Limonciello, Mario > > > Cc: dvhart@infradead.org; Andy Shevchenko ; > > > LKML ; platform-driver-x86@vger.kernel.org; > Andy > > > Lutomirski ; quasisec@google.com; pali.rohar@gmail.com; > > > rjw@rjwysocki.net; mjg59@google.com; hch@lst.de; Alan Cox > > > > > > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface > for > > > drivers > > > > > > On Thu, Oct 19, 2017 at 12:50:16PM -0500, Mario Limonciello wrote: > > > > + wblock = container_of(wdev, struct wmi_block, dev); > > > > + if (!wblock) > > > > + return -ENODEV; > > > > > > How can container_of() ever return NULL? If so, you have a very odd > > > memory layout... > > > > > > > I'm assuming this is from set_required_buffer_size right? > > > > The symbol is exported out for other drivers to use. It's possible for another > > driver to allocate a wmi_device structure that's not part of a wblock. > > container_of can never return NULL, it does arithmetics on a pointer > based on the type it is embedded into. > > You better don't register a wmi_device that's not part of the block > with your driver. Which others drivers are those, btw? No drivers do this today, it's obviously not a good idea. I was just saying it's hypothetical. I see that the other methods exported (wmi_evaluate_method and such) to drivers require that it's part of a wblock, so this seems like a reasonable expectation from other drivers. I'll remove this invalid check. > > This one it's possible that a driver isn't bound to a device, and when > > that happens wdriver is NULL. > See above, no it can't. Maybe wblock->dev.dev.driver can be NULL, > but in that case you must not call container_of on it. > container_of() is just pointer math. If you pass in NULL, you will get > a non-NULL value (incremented or decremented). If you pass in a very > tiny number, you might get NULL, but that's still really wrong. > > In other words, these tests will _NEVER_ fail. Go ahead, try it :) I was seeing failures (with NULL) when I tested with some drivers unbound, but I now understand my check is definitely wrong. I'll adjust the check and make sure it's valid. Thank you both for your feedback here.