From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756021Ab1AGCDf (ORCPT ); Thu, 6 Jan 2011 21:03:35 -0500 Received: from void.printf.net ([89.145.121.20]:33552 "EHLO void.printf.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756008Ab1AGCDc (ORCPT ); Thu, 6 Jan 2011 21:03:32 -0500 Date: Fri, 7 Jan 2011 02:03:26 +0000 From: Chris Ball To: Linus Torvalds Cc: Nick Piggin , Jongman Heo , linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [announce] vfs-scale git tree update Message-ID: <20110107020325.GA18808@void.printf.net> References: <20110105102534.GA6679@amd> <20110107005954.GA18145@void.printf.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 06, 2011 at 05:41:39PM -0800, Linus Torvalds wrote: > I'm wondering if this is a previously existing race condition leading > to a deadlock. One that previously would have been serialized enough > by the dcache lock that you'd never have that happen. > > It might be interesting to re-run it with mutex debugging and lockdep > enabled, to see if that reports anything. Although it probably won't, > because it's not about a plain lock dependency, but ends up being > deadlocked on the uevent being finished (but you have the modprobe and > the request_firmware ones waiting on each other). > > I dunno. I haven't really though that fully through. But we've had > cases roughly like that before, and yes, they can be exposed by some > independent serialization going away - long-standing potential bugs, > that simply never happened in practice before. Yeah, that sounds right: arch/x86/kernel/microcode_core.c: mutex_lock(µcode_mutex); ... error = sysdev_driver_register(&cpu_sysdev_class, &mc_sysdev_driver); (which calls request_microcode_fw() indirectly, and goes out to userspace.) I'm willing to have a try at making this lockless if no-one beats me to it, although it would need to wait until I've got the MMC merge out of the way. -- Chris Ball One Laptop Per Child