From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: Regression with suspicious RCU usage splats with cpu_pm change Date: Mon, 17 Jul 2017 05:39:38 -0700 Message-ID: <20170717123938.GP2393@linux.vnet.ibm.com> References: <20170713070749.GE16509@atomide.com> <20170713124318.GK2393@linux.vnet.ibm.com> <20170717060806.GC10026@atomide.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53169 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751335AbdGQMjo (ORCPT ); Mon, 17 Jul 2017 08:39:44 -0400 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6HCccDl133662 for ; Mon, 17 Jul 2017 08:39:44 -0400 Received: from e18.ny.us.ibm.com (e18.ny.us.ibm.com [129.33.205.208]) by mx0a-001b2d01.pphosted.com with ESMTP id 2brqmnq33s-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 17 Jul 2017 08:39:43 -0400 Received: from localhost by e18.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 17 Jul 2017 08:39:42 -0400 Content-Disposition: inline In-Reply-To: <20170717060806.GC10026@atomide.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Tony Lindgren Cc: Alex Shi , "Rafael J. Wysocki" , Linux Kernel Mailing List , Linux PM , Linux OMAP Mailing List , Catalin Marinas , Will Deacon On Sun, Jul 16, 2017 at 11:08:07PM -0700, Tony Lindgren wrote: > * Alex Shi [170716 16:25]: > > I reused the rcu_irq_enter_irqson() from RCU_NONIDLE to avoid this issue. > > It works fine. > > > > Tony, Could you like to give a tested-by if this patch works for you. > > Yeah that keeps things booting for me with no splats so: > > Tested-by: Tony Lindgren > > In general, it seems we're missing the knowledge in Linux kernel > of when the entire system is idle. Right now it seems that only > cpuidle_coupled knows that? > > We could probably simplify things by adding some PM state for > entire system idle. Then cpuidle code and timer code could use > that to test when it's safe to do whatever the SoC needs to do > to enter deeper power states. > > If we already have something like that, please do let me know :) Well, we used to have CONFIG_NO_HZ_FULL_SYSIDLE, which detected full-system idle lazily so as to avoid scalability bottlenecks. https://lwn.net/Articles/558284/ No one was using it, so I removed it last merge window. The patch that removed it is at sysidle.2017.05.11a, which can probably still be reverted cleanly. Or just use v4.11 or earlier. Thanx, Paul