From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754303AbbJGOS4 (ORCPT ); Wed, 7 Oct 2015 10:18:56 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:57920 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753235AbbJGOSz (ORCPT ); Wed, 7 Oct 2015 10:18:55 -0400 X-IBM-Helo: d03dlp01.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Wed, 7 Oct 2015 07:18:50 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Message-ID: <20151007141850.GD3910@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20151006161305.GA9799@linux.vnet.ibm.com> <1444148028-11551-1-git-send-email-paulmck@linux.vnet.ibm.com> <1444148028-11551-7-git-send-email-paulmck@linux.vnet.ibm.com> <20151006200725.GV3604@twins.programming.kicks-ass.net> <20151006201915.GV3910@linux.vnet.ibm.com> <20151006203224.GY3604@twins.programming.kicks-ass.net> <20151006210348.GY3910@linux.vnet.ibm.com> <20151007072038.GU2881@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151007072038.GU2881@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15100714-0005-0000-0000-000018C3DD9C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2015 at 09:20:38AM +0200, Peter Zijlstra wrote: > On Tue, Oct 06, 2015 at 02:03:48PM -0700, Paul E. McKenney wrote: > > On Tue, Oct 06, 2015 at 10:32:24PM +0200, Peter Zijlstra wrote: > > > On Tue, Oct 06, 2015 at 01:19:15PM -0700, Paul E. McKenney wrote: > > > > On Tue, Oct 06, 2015 at 10:07:25PM +0200, Peter Zijlstra wrote: > > > > > On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote: > > > > > > Currently, __srcu_read_lock() cannot be invoked from restricted > > > > > > environments because it contains calls to preempt_disable() and > > > > > > preempt_enable(), both of which can invoke lockdep, which is a bad > > > > > > idea in some restricted execution modes. This commit therefore moves > > > > > > the preempt_disable() and preempt_enable() from __srcu_read_lock() > > > > > > to srcu_read_lock(). It also inserts the preempt_disable() and > > > > > > preempt_enable() around the call to __srcu_read_lock() in do_exit(). > > > > > > > > > > Did you not simply want to use: preempt_disable_notrace() ? > > > > > > > > I believe that tracing the preempt_disable() in srcu_read_lock() and > > > > srcu_read_unlock() is actually a good thing. Or am I missing your > > > > point? > > > > > > Depends a bit on why we needed this change in the first place -- which, > > > going by the other branch of this thread, seems lost. However, > > > preempt_{dis,en}able_notrace() will not end up in any tracer/lockdep and > > > generate the minimum code that preserves the required semantics. > > > > True enough! But can all architectures locate the TIF in all contexts? > > They had better, otherwise we have a problem with NMIs touching it :-) Fair enough! ;-) Thanx, Paul