Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758933AbYAGR7x (ORCPT ); Mon, 7 Jan 2008 12:59:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756774AbYAGR7o (ORCPT ); Mon, 7 Jan 2008 12:59:44 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:37539 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756159AbYAGR7n (ORCPT ); Mon, 7 Jan 2008 12:59:43 -0500 From: "Rafael J. Wysocki" To: Alan Stern Subject: Re: [PATCH] PM: Acquire device locks on suspend Date: Mon, 7 Jan 2008 19:01:23 +0100 User-Agent: KMail/1.9.6 (enterprise 20070904.708012) Cc: Johannes Berg , Greg KH , Andrew Morton , Len Brown , Ingo Molnar , ACPI Devel Maling List , LKML , pm list References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200801071901.24926.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2092 Lines: 48 On Monday, 7 of January 2008, Alan Stern wrote: > On Mon, 7 Jan 2008, Rafael J. Wysocki wrote: > > > Please see the patch at: http://lkml.org/lkml/2008/1/6/298 . It represents my > > current idea about how to do that. > > It has some problems. > > First, note that the list manipulations in dpm_suspend(), > device_power_down(), and so on aren't protected by dpm_list_mtx. So > your patch could corrupt the list pointers. Yes, they need the locking. I have overlooked that, mostly because the locking was removed by gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch too (because you assumed there woundn't be any need to remove a device during a suspend, right?). > Are you assuming that no other threads can be running at this time? No, I'm not. > Note also that device_pm_destroy_suspended() does up(&dev->sem), but it > doesn't know whether or not dev->sem was locked to begin with. Do you mean it might have been released already by another thread calling device_pm_destroy_suspended() on the same device? > Do you want to rule out the possibility of a driver's suspend or remove > methods calling destroy_suspended_device() on its own device? With > your synchronous approach, this would mean that the suspend/resume > method would indirectly end up calling the remove method. This is > dangerous at best; with USB it would be a lockdep violation. With an > asynchronous approach, on the other hand, this wouldn't be a problem. Well, the asynchronous apprach has the problem that the device may end up on a wrong list when removed by one of the .suspend() callbacks (and I don't see how to avoid that without extra complexity). Perhaps that's something we can live with, though. One more question: is there any particular reason not to call device_pm_remove() at the beginning of device_del()? Rafael -- 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/