Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753215AbYJ0Hep (ORCPT ); Mon, 27 Oct 2008 03:34:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751781AbYJ0Heg (ORCPT ); Mon, 27 Oct 2008 03:34:36 -0400 Received: from mga09.intel.com ([134.134.136.24]:1969 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751591AbYJ0Heg (ORCPT ); Mon, 27 Oct 2008 03:34:36 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.33,491,1220252400"; d="scan'208";a="455763049" Message-ID: <49056EF6.3000904@intel.com> Date: Mon, 27 Oct 2008 15:34:14 +0800 From: "Zhao, Yu" User-Agent: Thunderbird 2.0.0.17 (Windows/20080914) MIME-Version: 1.0 To: Matthew Wilcox CC: Yu Zhao , Jesse Barnes , "linux-pci@vger.kernel.org" , "greg@kroah.com" , "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "stable@kernel.org" , Rakib Mullick Subject: Re: [PATCH] pci: Fixing drivers/pci/search.c compilation warning. References: <20080928163211.GR27204@parisc-linux.org> <20081021011308.GA3889@parisc-linux.org> <490467CD.3000402@uniscape.net> <20081026183412.GX26094@parisc-linux.org> <49053313.9080706@intel.com> <20081027070745.GY26094@parisc-linux.org> <49056A2F.6030206@intel.com> <20081027072137.GZ26094@parisc-linux.org> In-Reply-To: <20081027072137.GZ26094@parisc-linux.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1860 Lines: 44 Matthew Wilcox wrote: > On Mon, Oct 27, 2008 at 03:13:51PM +0800, Zhao, Yu wrote: >> Matthew Wilcox wrote: >>> On Mon, Oct 27, 2008 at 11:18:43AM +0800, Zhao, Yu wrote: >>>> Matthew Wilcox wrote: >>>>> Yes, that's why pci_find_device() is deprecated. But it doesn't also >>>>> need to be buggy ;-) >>>> How about pci_get_bus_and_slot()? People would meet the problem with it >>>> anyway. >>> What problem with it? It's documented to return the device with an >>> increased refcount, and the implementation appears to do exactly that: >>> >> The 'dev' returned by pci_get_device() may be destroyed by PCI hotplug. >> I suppose that passing this 'dev' to pci_get_device() in the next loop >> would crash the system, right? > > Erm, no, the 'dev' cannot be destroyed because the caller has a refcount > on it. The physical device backing it might have gone away. The dev Why does the caller have a reference count? I don't see we increase the reference count after the 'dev' is returned by following in pci_get_dev_by_id(): dev = bus_find_device(&pci_bus_type, dev_start, (void *)id, match_pci_dev_by_id); And this 'dev' becomes the 'from' in the next loop, but it may be destroyed before the 'pci_dev_get(from)', isn't it? > won't be destroyed until its reference count reaches zero, which could > be any time someone calls pci_dev_put() on it. In the scenario you're > postulating, it would happen in pci_get_dev_by_id(): > > if (from) > pci_dev_put(from); > > which is the last time that 'from' is referred to in that callchain. > -- 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/