From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752134AbdDFFU0 (ORCPT ); Thu, 6 Apr 2017 01:20:26 -0400 Received: from lelnx193.ext.ti.com ([198.47.27.77]:48361 "EHLO lelnx193.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751596AbdDFFUR (ORCPT ); Thu, 6 Apr 2017 01:20:17 -0400 Subject: Re: [PATCH v6 01/23] PCI: endpoint: Add EP core layer to enable EP controller and EP functions To: Bjorn Helgaas References: <20170405085243.18123-1-kishon@ti.com> <20170405085243.18123-2-kishon@ti.com> <20170405165254.GA17066@bhelgaas-glaptop.roam.corp.google.com> CC: Bjorn Helgaas , Joao Pinto , , , , , , , , From: Kishon Vijay Abraham I Message-ID: Date: Thu, 6 Apr 2017 10:49:17 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170405165254.GA17066@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Bjorn, On Wednesday 05 April 2017 10:22 PM, Bjorn Helgaas wrote: > On Wed, Apr 05, 2017 at 02:22:21PM +0530, Kishon Vijay Abraham I wrote: >> Introduce a new EP core layer in order to support endpoint functions in >> linux kernel. This comprises the EPC library (Endpoint Controller Library) >> and EPF library (Endpoint Function Library). EPC library implements >> functions specific to an endpoint controller and EPF library implements >> functions specific to an endpoint function. >> ... > >> +/** >> + * pci_epf_linkup() - Notify the function driver that EPC device has >> + * established a connection with the Root Complex. >> + * @epf: the EPF device bound to the EPC device which has established >> + * the connection with the host >> + * >> + * Invoke to notify the function driver that EPC device has established >> + * a connection with the Root Complex. >> + */ >> +void pci_epf_linkup(struct pci_epf *epf) >> +{ >> + if (!epf->driver) >> + dev_WARN(&epf->dev, "epf device not bound to driver\n"); >> + >> + epf->driver->ops->linkup(epf); > > I don't understand what's going on here. We warn if epf->driver is > NULL, but the next thing we do is dereference it. > > For NULL pointers that are symptoms of Linux defects, I usually prefer > not to check at all so that a dereference generates an oops and we can > debug the problem. For NULL pointers caused by user error, we would > generally return an error that percolates up to the user. > > I haven't competely wrapped my head around this endpoint support, but > I assume a NULL pointer here would be caused by user error, not > necessarily a Linux defect. So why would we dereference a NULL > pointer? And what happens when we do? Is this just going to oops an > embedded Linux running inside the endpoint? Is that the correct > behavior? With the new configfs directory structure, this should be a kernel error. However the EPF layer should be independent of how it's API's are used i.e someone can create a new sysfs/configfs structure and the value of epf->driver might be dependent on user actions. I think I'd prefer not to dereference NULL pointers since we anyways have a dev_WARN for debug. I'll resend this patch with return if epf->driver is NULL. Thanks Kishon From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kishon Vijay Abraham I Subject: Re: [PATCH v6 01/23] PCI: endpoint: Add EP core layer to enable EP controller and EP functions Date: Thu, 6 Apr 2017 10:49:17 +0530 Message-ID: References: <20170405085243.18123-1-kishon@ti.com> <20170405085243.18123-2-kishon@ti.com> <20170405165254.GA17066@bhelgaas-glaptop.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170405165254.GA17066-1RhO1Y9PlrlHTL0Zs8A6p5iNqAH0jzoTYJqu5kTmcBRl57MIdRCFDg@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Bjorn Helgaas Cc: Bjorn Helgaas , Joao Pinto , linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, nsekhar-l0cyMroinI0@public.gmane.org List-Id: devicetree@vger.kernel.org Hi Bjorn, On Wednesday 05 April 2017 10:22 PM, Bjorn Helgaas wrote: > On Wed, Apr 05, 2017 at 02:22:21PM +0530, Kishon Vijay Abraham I wrote: >> Introduce a new EP core layer in order to support endpoint functions in >> linux kernel. This comprises the EPC library (Endpoint Controller Library) >> and EPF library (Endpoint Function Library). EPC library implements >> functions specific to an endpoint controller and EPF library implements >> functions specific to an endpoint function. >> ... > >> +/** >> + * pci_epf_linkup() - Notify the function driver that EPC device has >> + * established a connection with the Root Complex. >> + * @epf: the EPF device bound to the EPC device which has established >> + * the connection with the host >> + * >> + * Invoke to notify the function driver that EPC device has established >> + * a connection with the Root Complex. >> + */ >> +void pci_epf_linkup(struct pci_epf *epf) >> +{ >> + if (!epf->driver) >> + dev_WARN(&epf->dev, "epf device not bound to driver\n"); >> + >> + epf->driver->ops->linkup(epf); > > I don't understand what's going on here. We warn if epf->driver is > NULL, but the next thing we do is dereference it. > > For NULL pointers that are symptoms of Linux defects, I usually prefer > not to check at all so that a dereference generates an oops and we can > debug the problem. For NULL pointers caused by user error, we would > generally return an error that percolates up to the user. > > I haven't competely wrapped my head around this endpoint support, but > I assume a NULL pointer here would be caused by user error, not > necessarily a Linux defect. So why would we dereference a NULL > pointer? And what happens when we do? Is this just going to oops an > embedded Linux running inside the endpoint? Is that the correct > behavior? With the new configfs directory structure, this should be a kernel error. However the EPF layer should be independent of how it's API's are used i.e someone can create a new sysfs/configfs structure and the value of epf->driver might be dependent on user actions. I think I'd prefer not to dereference NULL pointers since we anyways have a dev_WARN for debug. I'll resend this patch with return if epf->driver is NULL. Thanks Kishon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 From: kishon@ti.com (Kishon Vijay Abraham I) Date: Thu, 6 Apr 2017 10:49:17 +0530 Subject: [PATCH v6 01/23] PCI: endpoint: Add EP core layer to enable EP controller and EP functions In-Reply-To: <20170405165254.GA17066@bhelgaas-glaptop.roam.corp.google.com> References: <20170405085243.18123-1-kishon@ti.com> <20170405085243.18123-2-kishon@ti.com> <20170405165254.GA17066@bhelgaas-glaptop.roam.corp.google.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Bjorn, On Wednesday 05 April 2017 10:22 PM, Bjorn Helgaas wrote: > On Wed, Apr 05, 2017 at 02:22:21PM +0530, Kishon Vijay Abraham I wrote: >> Introduce a new EP core layer in order to support endpoint functions in >> linux kernel. This comprises the EPC library (Endpoint Controller Library) >> and EPF library (Endpoint Function Library). EPC library implements >> functions specific to an endpoint controller and EPF library implements >> functions specific to an endpoint function. >> ... > >> +/** >> + * pci_epf_linkup() - Notify the function driver that EPC device has >> + * established a connection with the Root Complex. >> + * @epf: the EPF device bound to the EPC device which has established >> + * the connection with the host >> + * >> + * Invoke to notify the function driver that EPC device has established >> + * a connection with the Root Complex. >> + */ >> +void pci_epf_linkup(struct pci_epf *epf) >> +{ >> + if (!epf->driver) >> + dev_WARN(&epf->dev, "epf device not bound to driver\n"); >> + >> + epf->driver->ops->linkup(epf); > > I don't understand what's going on here. We warn if epf->driver is > NULL, but the next thing we do is dereference it. > > For NULL pointers that are symptoms of Linux defects, I usually prefer > not to check at all so that a dereference generates an oops and we can > debug the problem. For NULL pointers caused by user error, we would > generally return an error that percolates up to the user. > > I haven't competely wrapped my head around this endpoint support, but > I assume a NULL pointer here would be caused by user error, not > necessarily a Linux defect. So why would we dereference a NULL > pointer? And what happens when we do? Is this just going to oops an > embedded Linux running inside the endpoint? Is that the correct > behavior? With the new configfs directory structure, this should be a kernel error. However the EPF layer should be independent of how it's API's are used i.e someone can create a new sysfs/configfs structure and the value of epf->driver might be dependent on user actions. I think I'd prefer not to dereference NULL pointers since we anyways have a dev_WARN for debug. I'll resend this patch with return if epf->driver is NULL. Thanks Kishon