Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932522AbaJHLyh (ORCPT ); Wed, 8 Oct 2014 07:54:37 -0400 Received: from mail-la0-f48.google.com ([209.85.215.48]:49396 "EHLO mail-la0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932343AbaJHLyd (ORCPT ); Wed, 8 Oct 2014 07:54:33 -0400 Date: Wed, 8 Oct 2014 13:54:28 +0200 From: Jiri Pirko To: "Paul E. McKenney" Cc: Joe Lawrence , Tejun Heo , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 1/2] workqueue: add quiescent state between work items Message-ID: <20141008115428.GA1858@nanopsycho.orion> References: <1412529862-17954-1-git-send-email-joe.lawrence@stratus.com> <1412529862-17954-2-git-send-email-joe.lawrence@stratus.com> <20141005192119.GE8549@htj.dyndns.org> <20141005194748.GG8549@htj.dyndns.org> <20141006042158.GW5015@linux.vnet.ibm.com> <20141007072942.GA2088@nanopsycho.orion> <20141007134329.GA4880@linux.vnet.ibm.com> <20141007134528.1a59f31b@jlaw-desktop.mno.stratus.com> <20141008032411.GG4880@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141008032411.GG4880@linux.vnet.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wed, Oct 08, 2014 at 05:24:11AM CEST, paulmck@linux.vnet.ibm.com wrote: >On Tue, Oct 07, 2014 at 01:45:28PM -0400, Joe Lawrence wrote: >> On Tue, 7 Oct 2014 06:43:29 -0700 >> "Paul E. McKenney" wrote: >> >> > On Tue, Oct 07, 2014 at 09:29:42AM +0200, Jiri Pirko wrote: >> [ ... snip ... ] >> > > >> > > Paul, Tehun, how do you propose to fix this on older kernels which do >> > > not have rcu_note_voluntary_context_switch? I'm particullary interested >> > > in 3.10. >> > >> > Hello, Jiri, >> > >> > Older kernels can instead use rcu_note_context_switch(). >> >> Hi Paul, >> >> Does 4a81e8328d37 ("rcu: Reduce overhead of cond_resched() checks for >> RCU") affect a backport to 3.10? >> >> I noticed that rcu_note_context_switch added a call to >> rcu_momentary_dyntick_idle in that change, which is only present in >> v3.16+. >> >> Would rcu_note_context_switch be effective by itself on a 3.10 kernel? > >Should be fine. There is more overhead than current mainline, but that >should not be in the noise compared to executing a work-queue item. > > Thanx, Paul > I cooked up following patch. Please tell me if it is fine or not. I can also send it oficially so it can be included into stable trees: Subject: workqueue: Add quiescent state between work items Similar to the stop_machine deadlock scenario on !PREEMPT kernels addressed in b22ce2785d97 "workqueue: cond_resched() after processing each work item", kworker threads requeueing back-to-back with zero jiffy delay can stall RCU. The cond_resched call introduced in that fix will yield only iff there are other higher priority tasks to run, so force a quiescent RCU state between work items. Signed-off-by: Jiri Pirko --- kernel/workqueue.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index e9719c7..14a7163 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2196,8 +2196,10 @@ __acquires(&pool->lock) * kernels, where a requeueing work item waiting for something to * happen could deadlock with stop_machine as such work item could * indefinitely requeue itself while all other CPUs are trapped in - * stop_machine. + * stop_machine. At the same time, report a quiescent RCU state so + * the same condition doesn't freeze RCU. */ + rcu_note_context_switch(raw_smp_processor_id()); cond_resched(); spin_lock_irq(&pool->lock); -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/