From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756038Ab2CJCDU (ORCPT ); Fri, 9 Mar 2012 21:03:20 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:18487 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755868Ab2CJCDO (ORCPT ); Fri, 9 Mar 2012 21:03:14 -0500 X-Authority-Analysis: v=2.0 cv=M9vP2lMs c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=mx00zOLDafsA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=1fitlbfCT6V4qjbYaA0A:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1331344992.25686.612.camel@gandalf.stny.rr.com> Subject: Re: 3.0.23-rt39 BUG: scheduling while atomic, _cpu_down() From: Steven Rostedt To: frank.rowand@am.sony.com Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org Date: Fri, 09 Mar 2012 21:03:12 -0500 In-Reply-To: <4F5AB3B6.2040705@am.sony.com> References: <4F5AB3B6.2040705@am.sony.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-03-09 at 17:51 -0800, Frank Rowand wrote: > Hi Thomas, > (and Steve, since you've been mucking about in the hotplug code,) > > Yet another bit of fallout related to hotplug. > > This appears to affect 3.0-rt1, 3.0.23-rt29, and 3.2.9-rt17. > (Thus probably all 3.x versions, but I haven't been masochistic > enough to check.) > > If not defined CONFIG_PREEMPT_RT_FULL then So you're saying that there's a bug with PREEMPT_RT off? > > - hotplug_lock() is a mutex_lock() > - cpu_hotplug_begin() calls hotplug_lock() > - _cpu_down() calls cpu_hotplug_begin() with preemption > disabled (disabled by the migrate_disable()) > > The call to cpu_hotplug_begin() is not in a preempt disabled > region until hotplug-use-migrate-disable.patch. This patch > moves the preempt_enable() (aka migrate_enable()) from just > before calling cpu_hotplug_begin() to after "out_cancel:". > > The BUG can be triggered by: > > echo 0 > /sys/devices/system/cpu/cpu1/online Note, there's a lot more wrong with hotplug in rt than this. The hotplug code really needs a total rewrite for RT to work with it. It probably should have a total rewrite in mainline anyway. -- Steve