Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758533Ab0FUUlR (ORCPT ); Mon, 21 Jun 2010 16:41:17 -0400 Received: from ist.d-labs.de ([213.239.218.44]:53326 "EHLO mx01.d-labs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758505Ab0FUUlE (ORCPT ); Mon, 21 Jun 2010 16:41:04 -0400 Date: Mon, 21 Jun 2010 22:40:23 +0200 From: Florian Mickler To: Alan Stern Cc: "Rafael J. Wysocki" , Linux-pm mailing list , Matthew Garrett , Linux Kernel Mailing List , Dmitry Torokhov , Arve =?ISO-8859-15?Q?Hj=F8nnev=E5g?= , Neil Brown , mark gross <640e9920@gmail.com> Subject: Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend Message-ID: <20100621224023.0b14cde7@schatten.dmk.lab> In-Reply-To: References: <20100621073233.3f874ad0@schatten.dmk.lab> X-Mailer: Claws Mail 3.7.5 (GTK+ 2.18.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1485 Lines: 40 On Mon, 21 Jun 2010 12:54:44 -0400 (EDT) Alan Stern wrote: > On Mon, 21 Jun 2010, Florian Mickler wrote: > > > > > > What happens if an event arrives just before you read > > > > > /sys/power/wakeup_count, but the userspace consumer doesn't realize > > > > > there is a new unprocessed event until after the power manager checks > > > > > it? > > > > > > > I think this is not the kernel's problem. In this approach the kernel makes it > > > > possible for the user space to avoid the race. Whether or not the user space > > > > will use this opportunity is a different matter. > > > > > > It is _not_ possible for userspace to avoid this race. Help from the > > > kernel is needed. > > > > It is possible if every (relevant) userspace program implements a > > callback for the powermanager to check if one of it's wakeup-sources > > got activated. > > > > That way the powermanager would read /sys/power/wakeup_count, then do > > the roundtrip to all it's registered users and only then suspend. > > After further thought, there's still a race: Ah, yes. That's what I meant in my other mail with 'how to determine that an wake event is in flight'. Read this too late. > Alan Stern Cheers, Flo -- 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/