From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:57358 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751186AbdJMQdo (ORCPT ); Fri, 13 Oct 2017 12:33:44 -0400 Date: Fri, 13 Oct 2017 18:33:52 +0200 From: Greg KH To: "Paul E. McKenney" Cc: stable@vger.kernel.org, rostedt@goodmis.org Subject: Re: [PATCH -stable] rcu: Allow for page faults in NMI handlers Message-ID: <20171013163352.GA7914@kroah.com> References: <20171012230928.GA31473@linux.vnet.ibm.com> <20171013095245.GA31636@kroah.com> <20171013162543.GZ3521@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171013162543.GZ3521@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: 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 :) I'll go apply this now, sorry for the noise, and thanks for checking and the backport. greg k-h