From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756484AbcA2P1w (ORCPT ); Fri, 29 Jan 2016 10:27:52 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:45918 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756225AbcA2P1v (ORCPT ); Fri, 29 Jan 2016 10:27:51 -0500 Date: Fri, 29 Jan 2016 16:27:35 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Thomas Gleixner , Sasha Levin , LKML Subject: Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected Message-ID: <20160129152735.GB407@worktop> References: <20160113161608.GN3818@linux.vnet.ibm.com> <20160114181846.GZ3818@linux.vnet.ibm.com> <20160115014232.GQ3818@linux.vnet.ibm.com> <20160115211125.GA3818@linux.vnet.ibm.com> <20160115221045.GA8598@linux.vnet.ibm.com> <20160115231410.GA16973@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160115231410.GA16973@linux.vnet.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 15, 2016 at 03:14:10PM -0800, Paul E. McKenney wrote: > And if I make the scheduling-clock interrupt send extra wakeups to the RCU > grace-period kthread when needed, things work even with CPU hotplug going. > > The "when needed" means any time that the RCU grace-period kthread has > been sleeping three times as long as the timeout interval. If the first > wakeup does nothing, it does another wakeup once per second. > > So it looks like this change makes an existing problem much worse, as > opposed to introducing a new problem. I have a vague idea about a possible race window. Have you been observing this on PPC or x86? The reason I'm asking is that PPC (obviously) allows for more races :-)