From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52306 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752592AbdJLXOz (ORCPT ); Thu, 12 Oct 2017 19:14:55 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9CNDxk1052459 for ; Thu, 12 Oct 2017 19:14:54 -0400 Received: from e11.ny.us.ibm.com (e11.ny.us.ibm.com [129.33.205.201]) by mx0b-001b2d01.pphosted.com with ESMTP id 2djegkq5e9-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 12 Oct 2017 19:14:54 -0400 Received: from localhost by e11.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 12 Oct 2017 19:14:54 -0400 Date: Thu, 12 Oct 2017 16:14:52 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: gregkh@linuxfoundation.org, stable@vger.kernel.org Subject: Re: FAILED: patch "[PATCH] rcu: Allow for page faults in NMI handlers" failed to apply to 4.9-stable tree Reply-To: paulmck@linux.vnet.ibm.com References: <150694467720921@kroah.com> <20171002153317.245a2327@gandalf.local.home> <20171002193857.GV3521@linux.vnet.ibm.com> <20171002154748.1f1227c2@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171002154748.1f1227c2@gandalf.local.home> Message-Id: <20171012231452.GU3521@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: On Mon, Oct 02, 2017 at 03:47:48PM -0400, Steven Rostedt wrote: > On Mon, 2 Oct 2017 12:38:57 -0700 > "Paul E. McKenney" wrote: > > > On Mon, Oct 02, 2017 at 03:33:17PM -0400, Steven Rostedt wrote: > > > > > > Paul, > > > > > > Can you backport this patch to 4.9 and 4.4 if it is required. The other > > > patches I posted (and also failed to apply, but should be backported) > > > depend on this patch, if it is an issue with those kernels. > > > > No problem! > > > > How do we determine whether or not it is required? > > Can rcu_irq_enter() be called within a rcu_nmi_enter() in these > kernels? If not, that needs to be fixed. Because nmi's can still page > fault. > > > > > Do we need to ask one of Bruce or Nick? ;-) > > > > The bug I fixed is actually there, but lockdep doesn't complain. The > module code that uses synchronize_sched() which requires RCU to be > watching when preemption is disabled. RCU isn't watching is some of > these cases that are called. Recent kernels added rcu annotations into > these preempt disabled paths which caused lockdep to report the issue. > The older kernels that had the bug just didn't have lockdep complain > about it. It turned out that one backport is needed for 4.2-4.4, and another for 4.5-4.12. I sent both. Thanx, Paul