Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753038AbYJ0HWF (ORCPT ); Mon, 27 Oct 2008 03:22:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751838AbYJ0HVz (ORCPT ); Mon, 27 Oct 2008 03:21:55 -0400 Received: from palinux.external.hp.com ([192.25.206.14]:47794 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751718AbYJ0HVy (ORCPT ); Mon, 27 Oct 2008 03:21:54 -0400 Date: Mon, 27 Oct 2008 01:21:38 -0600 From: Matthew Wilcox To: "Zhao, Yu" 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. Message-ID: <20081027072137.GZ26094@parisc-linux.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49056A2F.6030206@intel.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1624 Lines: 38 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 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. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- 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/