Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756032Ab3IZJ32 (ORCPT ); Thu, 26 Sep 2013 05:29:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21469 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751121Ab3IZJ30 (ORCPT ); Thu, 26 Sep 2013 05:29:26 -0400 Date: Thu, 26 Sep 2013 11:27:24 +0200 From: Veaceslav Falico To: Bjorn Helgaas Cc: Neil Horman , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , Greg Kroah-Hartman Subject: Re: [PATCH 1/3] msi: add forgotten pci_dev_put(pdev) to populate_msi_sysfs() Message-ID: <20130926092724.GA4783@redhat.com> References: <1379382464-7920-1-git-send-email-vfalico@redhat.com> <1379382464-7920-2-git-send-email-vfalico@redhat.com> <20130925232300.GA7368@neilslaptop.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4124 Lines: 97 On Wed, Sep 25, 2013 at 05:35:54PM -0600, Bjorn Helgaas wrote: >On Wed, Sep 25, 2013 at 5:23 PM, Neil Horman wrote: >> On Wed, Sep 25, 2013 at 03:08:05PM -0600, Bjorn Helgaas wrote: >>> [+cc Neil (he added this code in da8d1c8ba4), Greg] >>> >>> On Mon, Sep 16, 2013 at 7:47 PM, Veaceslav Falico wrote: >>> > Before trying to kobject_init_and_add(), we add a reference to pdev via >>> > pci_dev_get(pdev). However, if it fails to init and/or add the kobject, we >>> > don't return it back - even on out_unroll. >>> > >>> > Fix this by adding pci_dev_put(pdev) before going to unrolling section. >>> > >>> > CC: Bjorn Helgaas >>> > CC: linux-pci@vger.kernel.org >>> > CC: linux-kernel@vger.kernel.org >>> > Signed-off-by: Veaceslav Falico >>> > --- >>> > drivers/pci/msi.c | 4 +++- >>> > 1 file changed, 3 insertions(+), 1 deletion(-) >>> > >>> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c >>> > index d5f90d6..14bf578 100644 >>> > --- a/drivers/pci/msi.c >>> > +++ b/drivers/pci/msi.c >>> > @@ -534,8 +534,10 @@ static int populate_msi_sysfs(struct pci_dev *pdev) >>> > pci_dev_get(pdev); >>> > ret = kobject_init_and_add(kobj, &msi_irq_ktype, NULL, >>> > "%u", entry->irq); >>> > - if (ret) >>> > + if (ret) { >>> > + pci_dev_put(pdev); >>> > goto out_unroll; >>> > + } >>> > >>> > count++; >>> > } >>> >>> I don't understand why this code does the pci_dev_get() in the first >>> place. The pdev->msi_list of msi_desc structs is private to the >>> pci_dev, and even without bumping the refcount, there should be no way >>> for the pci_dev to be freed before the msi_desc. >>> >> Its been a few years now, but IIRC I did the pci_dev_get/put here to ensure that >> people didn't try to remove the device prior to freeing all their interrupts >> (i.e I didn't want a broken driver to go through its remove routine without >> freeing all its irqs). That might have been the wrong thing to do, but thats >> what bubbles to the front of my head when looking at this. > >That sounds plausible, but I think I'd rather deal with that by having >the PCI core remove logic free all the interrupts. I *think* that's >already in place, i.e., pci_free_resources() calls >msi_remove_pci_irq_vectors(). So I propose that we remove the >pci_dev_get()/put() unless we come up with a more compelling reason >for it. > >>> I also don't understand this nearby code (the same pattern appears in >>> free_msi_irqs()): >>> >>> out_unroll: >>> list_for_each_entry(entry, &pdev->msi_list, list) { >>> if (!count) >>> break; >>> kobject_del(&entry->kobj); >>> kobject_put(&entry->kobj); >>> count--; >>> } >>> >>> Why do we call kobject_del() here? The kobject_put() will call >>> kobject_del() anyway, so it looks redundant. >>> Documentation/kobject.txt says kobject_del() must be called explicitly >>> to break a circular reference, but I don't think we have that here. >>> >> I think thats exactly why I did it, because of the documentation. I agree >> however, it does look redundant. Harmless, but redundant. > >OK, thanks. I think we should remove it on the grounds that it's not >needed and removing it will make this code look more similar to other >callers of kobject_init_and_add(), which means bugs will have fewer >places to hide. Hi, Sounds great, I'll add this as new patches and send this in a separate patchset with the unregister msi_kset in free_msi_irqs patch, so that it won't depend on the fix (both removing kobject_del() and pci_dev_get/put()). Thank you! > >Thanks, Neil! > >Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/