From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752379AbaBGONQ (ORCPT ); Fri, 7 Feb 2014 09:13:16 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:43082 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751785AbaBGONP (ORCPT ); Fri, 7 Feb 2014 09:13:15 -0500 Date: Fri, 7 Feb 2014 09:13:13 -0500 From: Steven Rostedt To: Steven Rostedt Cc: Sebastian Andrzej Siewior , LKML , linux-rt-users , Thomas Gleixner , Clark Williams , "Luis Claudio R. Goncalves" , John Kacur , Ulrich Obergfell Subject: Re: [PATCH RT] rt: Make cpu_chill() use hrtimer instead of msleep() Message-ID: <20140207091313.097f9059@gandalf.local.home> In-Reply-To: <20140207090834.72774272@gandalf.local.home> References: <20140205115125.3cc950ce@gandalf.local.home> <20140207113006.GD23668@linutronix.de> <20140207090834.72774272@gandalf.local.home> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 7 Feb 2014 09:08:34 -0500 Steven Rostedt wrote: > > could you please tell me which two locks are invovled here? I should have also stated that it was only one lock that was involved. But the lock owner was doing a msleep() that requires a wakeup by ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock held by the msleep() caller, then you have your deadlock. It's best not to have any softirqs going to sleep requiring another softirq to wake it up. Note, if we ever require a timer softirq to do a cpu_chill() it will most definitely hit this deadlock. -- Steve