Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755617Ab3IYXgS (ORCPT ); Wed, 25 Sep 2013 19:36:18 -0400 Received: from mail-ie0-f180.google.com ([209.85.223.180]:36575 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061Ab3IYXgQ (ORCPT ); Wed, 25 Sep 2013 19:36:16 -0400 MIME-Version: 1.0 In-Reply-To: <20130925232300.GA7368@neilslaptop.think-freely.org> 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> From: Bjorn Helgaas Date: Wed, 25 Sep 2013 17:35:54 -0600 Message-ID: Subject: Re: [PATCH 1/3] msi: add forgotten pci_dev_put(pdev) to populate_msi_sysfs() To: Neil Horman Cc: Veaceslav Falico , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , Greg Kroah-Hartman Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3740 Lines: 87 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. 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/