From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:53830 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750973AbdJMJwh (ORCPT ); Fri, 13 Oct 2017 05:52:37 -0400 Date: Fri, 13 Oct 2017 11:52:45 +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: <20171013095245.GA31636@kroah.com> References: <20171012230928.GA31473@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171012230928.GA31473@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: 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? thanks, greg k-h