From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965576AbdJQS7R (ORCPT ); Tue, 17 Oct 2017 14:59:17 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:49268 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750992AbdJQS7P (ORCPT ); Tue, 17 Oct 2017 14:59:15 -0400 X-Google-Smtp-Source: ABhQp+Qpne9Nx8ECEFrwqt4Uge9h7pCe0blAH4f2OPkRPMMS5qDUaPcpwEpfJSMAgWmT10hYOkkdQg== Date: Tue, 17 Oct 2017 20:59:12 +0200 From: Pali =?utf-8?B?Um9ow6Fy?= To: Mario Limonciello Cc: dvhart@infradead.org, Andy Shevchenko , LKML , platform-driver-x86@vger.kernel.org, Andy Lutomirski , quasisec@google.com, rjw@rjwysocki.net, mjg59@google.com, hch@lst.de, Greg KH , Alan Cox Subject: Re: [PATCH v9 05/17] platform/x86: dell-wmi-descriptor: split WMI descriptor into it's own driver Message-ID: <20171017185912.uys7e7embiv4g3ii@pali> References: <892677197340c05a67e112884cc00ea938d33e91.1508259916.git.mario.limonciello@dell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <892677197340c05a67e112884cc00ea938d33e91.1508259916.git.mario.limonciello@dell.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 17 October 2017 13:21:49 Mario Limonciello wrote: > +struct descriptor_priv { > + struct list_head list; > + u32 interface_version; > + u32 size; > +}; > +static LIST_HEAD(wmi_list); > + > +bool dell_wmi_get_interface_version(u32 *version) > +{ > + struct descriptor_priv *priv; > + > + priv = list_first_entry_or_null(&wmi_list, > + struct descriptor_priv, > + list); > + if (!priv) > + return false; > + *version = priv->interface_version; There is a race condition. dell_wmi_descriptor_remove can be called between list_first_entry_or_null and dereferencing priv pointer. > + return true; > +} > +EXPORT_SYMBOL_GPL(dell_wmi_get_interface_version); > + > +bool dell_wmi_get_size(u32 *size) > +{ > + struct descriptor_priv *priv; > + > + priv = list_first_entry_or_null(&wmi_list, > + struct descriptor_priv, > + list); > + if (!priv) > + return false; > + *size = priv->size; And same there. > + return true; > +} > +EXPORT_SYMBOL_GPL(dell_wmi_get_size); ... > @@ -733,9 +659,8 @@ static int dell_wmi_probe(struct wmi_device *wdev) > return -ENOMEM; > dev_set_drvdata(&wdev->dev, priv); > > - err = dell_wmi_check_descriptor_buffer(wdev); > - if (err) > - return err; > + if (!dell_wmi_get_interface_version(&priv->interface_version)) > + return -EPROBE_DEFER; This could lead to another problem, when Dell decide to change WMI API and would not provide descriptor WMI GUID anymore, but still provide even WMI GUID. Basically it is needed to distinguish between states: 1) probe function of dell-wmi was called before probe function of dell-wmi-descriptor device initialization 2) probe function of dell-wmi was called, but there is no device instance of dell-wmi-descriptor 3) there is a device instance of dell-wmi-descriptor, but device is not registered to dell-wmi-descriptor driver, e.g. because userspace decided to forbid such thing, or because probing of dell-wmi-descriptor device failed 4) probe function of dell-wmi was called after probe function of dell-wmi-descriptor successfully I do not know how to handle such situation other drivers or how to do it correctly. I just wanted to show the fact that binding device <--> driver can fail in linux kernel (for more reasons) and in some cases repeating it does not make sense... Maybe other developers would comment this part? > > return dell_wmi_input_setup(wdev); > } -- Pali Rohár pali.rohar@gmail.com