From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43964 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751138AbdJMQsF (ORCPT ); Fri, 13 Oct 2017 12:48:05 -0400 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9DGi8TN026865 for ; Fri, 13 Oct 2017 12:48:05 -0400 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2djynd4b91-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 13 Oct 2017 12:48:05 -0400 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 13 Oct 2017 12:48:04 -0400 Date: Fri, 13 Oct 2017 09:48:01 -0700 From: "Paul E. McKenney" To: Greg KH Cc: stable@vger.kernel.org, rostedt@goodmis.org Subject: Re: [PATCH -stable] rcu: Allow for page faults in NMI handlers Reply-To: paulmck@linux.vnet.ibm.com References: <20171012230928.GA31473@linux.vnet.ibm.com> <20171013095245.GA31636@kroah.com> <20171013162543.GZ3521@linux.vnet.ibm.com> <20171013163352.GA7914@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171013163352.GA7914@kroah.com> Message-Id: <20171013164801.GC3521@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: On Fri, Oct 13, 2017 at 06:33:52PM +0200, Greg KH wrote: > On Fri, Oct 13, 2017 at 09:25:43AM -0700, Paul E. McKenney wrote: > > On Fri, Oct 13, 2017 at 11:52:45AM +0200, Greg KH wrote: > > > On Thu, Oct 12, 2017 at 04:09:28PM -0700, Paul E. McKenney wrote: > > > > A number of architecture invoke rcu_irq_enter() on exception entry in > > > > order to allow RCU read-side critical sections in the exception handler > > > > when the exception is from an idle or nohz_full CPU. This works, at > > > > least unless the exception happens in an NMI handler. In that case, > > > > rcu_nmi_enter() would already have exited the extended quiescent state, > > > > which would mean that rcu_irq_enter() would (incorrectly) cause RCU > > > > to think that it is again in an extended quiescent state. This will > > > > in turn result in lockdep splats in response to later RCU read-side > > > > critical sections. > > > > > > > > This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to > > > > take no action if there is an rcu_nmi_enter() in effect, thus avoiding > > > > the unscheduled return to RCU quiescent state. This in turn should > > > > make the kernel safe for on-demand RCU voyeurism. > > > > > > > > Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com > > > > > > > > Cc: stable@vger.kernel.org # 4.2.x > > > > Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") > > > > Reported-by: Steven Rostedt > > > > Signed-off-by: Paul E. McKenney > > > > Signed-off-by: Steven Rostedt (VMware) > > > > > > This does not apply to the 4.4-stable tree, was this the correct patch I > > > should be using for that tree? > > > > Hmmm... Idiot here backported to v4.4 in Linus's tree, which of > > course might not work... But it applies to v4.4.92 of -stable: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git > > > > Am I still applying it in the wrong place? > > Ugh, no, you are doing the right thing. I don't know what failed on my > end, that's what I get for trying to deal with RCU early in the morning > :) Believe me, I know that feeling very well! ;-) Thanx, Paul > I'll go apply this now, sorry for the noise, and thanks for checking and > the backport. > > greg k-h >