From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757971Ab2IDXDo (ORCPT ); Tue, 4 Sep 2012 19:03:44 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:33122 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757871Ab2IDXDn (ORCPT ); Tue, 4 Sep 2012 19:03:43 -0400 Date: Tue, 4 Sep 2012 16:03:25 -0700 From: "Paul E. McKenney" To: Josh Triplett Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() Message-ID: <20120904230325.GV2593@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346352988-32444-13-git-send-email-paulmck@linux.vnet.ibm.com> <20120831183431.GK4259@jtriplet-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120831183431.GK4259@jtriplet-mobl1> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12090423-7606-0000-0000-000003599EE3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 31, 2012 at 11:34:31AM -0700, Josh Triplett wrote: > On Thu, Aug 30, 2012 at 11:56:26AM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" > > > > The use of raw_local_irq_save() is unnecessary, given that local_irq_save() > > really does disable interrupts. Also, it appears to interfere with lockdep. > > Therefore, this commit moves to local_irq_save(). > > It looks like the non-raw versions also include tracing, which typically > has recursive dependency problems with RCU. Can all of these call sites > safely call into tracing without recursing back into RCU? The rcu_trace_sub_qlen() version is the most suspicious, but it is the one that Fengguang found to be causing the problem: https://lkml.org/lkml/2012/8/21/551 Thanx, Paul > - Josh Triplett > > > Reported-by: Fengguang Wu > > Signed-off-by: Paul E. McKenney > > Signed-off-by: Paul E. McKenney > > Tested-by: Fengguang Wu > > --- > > kernel/rcutiny_plugin.h | 10 +++++----- > > 1 files changed, 5 insertions(+), 5 deletions(-) > > > > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h > > index 918fd1e..3d01902 100644 > > --- a/kernel/rcutiny_plugin.h > > +++ b/kernel/rcutiny_plugin.h > > @@ -278,7 +278,7 @@ static int rcu_boost(void) > > rcu_preempt_ctrlblk.exp_tasks == NULL) > > return 0; /* Nothing to boost. */ > > > > - raw_local_irq_save(flags); > > + local_irq_save(flags); > > > > /* > > * Recheck with irqs disabled: all tasks in need of boosting > > @@ -287,7 +287,7 @@ static int rcu_boost(void) > > */ > > if (rcu_preempt_ctrlblk.boost_tasks == NULL && > > rcu_preempt_ctrlblk.exp_tasks == NULL) { > > - raw_local_irq_restore(flags); > > + local_irq_restore(flags); > > return 0; > > } > > > > @@ -317,7 +317,7 @@ static int rcu_boost(void) > > t = container_of(tb, struct task_struct, rcu_node_entry); > > rt_mutex_init_proxy_locked(&mtx, t); > > t->rcu_boost_mutex = &mtx; > > - raw_local_irq_restore(flags); > > + local_irq_restore(flags); > > rt_mutex_lock(&mtx); > > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ > > > > @@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) > > { > > unsigned long flags; > > > > - raw_local_irq_save(flags); > > + local_irq_save(flags); > > rcp->qlen -= n; > > - raw_local_irq_restore(flags); > > + local_irq_restore(flags); > > } > > > > /* > > -- > > 1.7.8 > > >