Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261541AbVCaQYU (ORCPT ); Thu, 31 Mar 2005 11:24:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261544AbVCaQYU (ORCPT ); Thu, 31 Mar 2005 11:24:20 -0500 Received: from ida.rowland.org ([192.131.102.52]:4612 "HELO ida.rowland.org") by vger.kernel.org with SMTP id S261541AbVCaQYR (ORCPT ); Thu, 31 Mar 2005 11:24:17 -0500 Date: Thu, 31 Mar 2005 11:24:17 -0500 (EST) From: Alan Stern X-X-Sender: stern@ida.rowland.org To: Patrick Mochel cc: David Brownell , Kernel development list Subject: Re: klists and struct device semaphores In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1506 Lines: 36 On Wed, 30 Mar 2005, Patrick Mochel wrote: > > Having thought it through, I believe all we need for USB support is this: > > > > Whenever usb_register() in the USB core calls driver_register() > > and the call filters down to driver_attach(), that routine > > should lock dev->parent->sem before calling driver_probe_device() > > (and unlock it afterward, of course). > > > > (For the corresponding remove pathway, where usb_deregister() > > calls driver_unregister(), it would be nice if __remove_driver() > > locked dev->parent->sem before calling device_release_driver(). > > This is not really needed, however, since USB drivers aren't > > supposed to touch the device in their disconnect() method.) > > > Why can't you just lock it in ->probe() and ->remove() yourself? Aha! There you go... This explains why you need explicit locking rules. When probe() and remove() are called, the driver-model core already owns the device's lock. If the driver then tried to lock the parent, it would mean acquiring locks in the wrong order. This could easily lead to deadlock. Furthermore, it will often happen during probe() and remove() that the parent's lock is already owned by the USB core. So the driver _mustn't_ try to lock it. Alan Stern - 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/