From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967023AbdEWSDp (ORCPT ); Tue, 23 May 2017 14:03:45 -0400 Received: from foss.arm.com ([217.140.101.70]:55414 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966970AbdEWSDk (ORCPT ); Tue, 23 May 2017 14:03:40 -0400 Subject: Re: [PATCH v4 1/2] PCI: Add tango MSI controller support To: Mason , Bjorn Helgaas Cc: Marc Gonzalez , Marc Zyngier , Thomas Gleixner , Jiang Liu , Lorenzo Pieralisi , Liviu Dudau , David Laight , linux-pci , Linux ARM , Thibaud Cornic , Phuong Nguyen , LKML References: <1f6b50c7-4887-838e-8c7d-c014d82b6d8e@sigmadesigns.com> <8e56647d-3b2d-9bfc-b59e-79a2efaa7826@sigmadesigns.com> <20170523170319.GB24431@bhelgaas-glaptop.roam.corp.google.com> From: Robin Murphy Message-ID: Date: Tue, 23 May 2017 19:03:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/05/17 18:54, Mason wrote: > On 23/05/2017 19:03, Bjorn Helgaas wrote: >> On Wed, May 17, 2017 at 04:56:08PM +0200, Marc Gonzalez wrote: >>> On 20/04/2017 16:28, Marc Gonzalez wrote: >>> >>>> +static int tango_set_affinity(struct irq_data *data, >>>> + const struct cpumask *mask, bool force) >>>> +{ >>>> + return -EINVAL; >>>> +} >>>> + >>>> +static struct irq_chip tango_chip = { >>>> + .irq_ack = tango_ack, >>>> + .irq_mask = tango_mask, >>>> + .irq_unmask = tango_unmask, >>>> + .irq_set_affinity = tango_set_affinity, >>>> + .irq_compose_msi_msg = tango_compose_msi_msg, >>>> +}; >>> >>> Hmmm... I'm wondering why .irq_set_affinity is required. >>> >>> static int setup_affinity(struct irq_desc *desc, struct cpumask *mask) >>> first calls __irq_can_set_affinity() to check whether >>> desc->irq_data.chip->irq_set_affinity) exists. >>> >>> then calls irq_do_set_affinity(&desc->irq_data, mask, false); >>> which calls chip->irq_set_affinity(data, mask, force); >>> = msi_domain_set_affinity() >>> which calls parent->chip->irq_set_affinity() unconditionally. >>> >>> Would it make sense to test that the callback is implemented >>> before calling it? >>> >>> >>> [ 0.723895] Unable to handle kernel NULL pointer dereference at virtual address 00000000 >> >> I'm not sure what you're asking. >> >> Is this a bug report for the v4 tango driver? > > No. > >> Or are you asking whether msi_domain_set_affinity() should be changed >> to check whether parent->chip->irq_set_affinity is implemented? > > Yes. The way things are implemented now, drivers are forced > to define an irq_set_affinity callback, even if it just returns > an error, otherwise, the kernel crashes, because of the > unconditional function pointer deref. > >> msi_domain_set_affinity() has called parent->chip->irq_set_affinity() >> without checking since it was added in 2014 by f3cf8bb0d6c3 ("genirq: Add >> generic msi irq domain support"), so if there's a problem here, it's most >> likely in the tango code. > > The issue is having to define an "empty" function. > (Unnecessary code bloat and maintenance.) AFAICS, only one driver (other than this one) implements a "do nothing" set_affinity callback - everyone else who doesn't do anything hardware specific just passes it along via irq_chip_set_affinity_parent(). Robin. > > I'll send a patch illustrating exactly what I intended. > > Regards. >