From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965841AbdCWQww (ORCPT ); Thu, 23 Mar 2017 12:52:52 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38167 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756379AbdCWQwu (ORCPT ); Thu, 23 Mar 2017 12:52:50 -0400 Date: Thu, 23 Mar 2017 09:52:44 -0700 From: "Paul E. McKenney" To: efault@gmx.de, tglx@linutronix.de, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, mingo@kernel.org, hpa@zytor.com, peterz@infradead.org Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/urgent] sched/clock: Fix clear_sched_clock_stable() preempt wobbly Reply-To: paulmck@linux.vnet.ibm.com References: <20170313124621.GA3328@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17032316-0048-0000-0000-000001399CA8 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006835; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000206; SDB=6.00837866; UDB=6.00411950; IPR=6.00615628; BA=6.00005234; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014779; XFM=3.00000013; UTC=2017-03-23 16:52:47 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17032316-0049-0000-0000-00003FED40A1 Message-Id: <20170323165244.GF3637@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-23_15:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703230148 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 23, 2017 at 02:10:47AM -0700, tip-bot for Peter Zijlstra wrote: > Commit-ID: 71fdb70eb48784c1f28cdf2e67c4c587dd7f2594 > Gitweb: http://git.kernel.org/tip/71fdb70eb48784c1f28cdf2e67c4c587dd7f2594 > Author: Peter Zijlstra > AuthorDate: Mon, 13 Mar 2017 13:46:21 +0100 > Committer: Ingo Molnar > CommitDate: Thu, 23 Mar 2017 07:31:48 +0100 > > sched/clock: Fix clear_sched_clock_stable() preempt wobbly > > Paul reported a problems with clear_sched_clock_stable(). Since we run > all of __clear_sched_clock_stable() from workqueue context, there's a > preempt problem. > > Solve it by only running the static_key_disable() from workqueue. > > Reported-by: Paul E. McKenney > Signed-off-by: Peter Zijlstra (Intel) > Cc: Linus Torvalds > Cc: Mike Galbraith > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: fweisbec@gmail.com > Link: http://lkml.kernel.org/r/20170313124621.GA3328@twins.programming.kicks-ass.net > Signed-off-by: Ingo Molnar For whatever it is worth given that it is already in -tip: Tested-by: Paul E. McKenney > --- > kernel/sched/clock.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c > index a08795e..fec0f58 100644 > --- a/kernel/sched/clock.c > +++ b/kernel/sched/clock.c > @@ -141,7 +141,14 @@ static void __set_sched_clock_stable(void) > tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); > } > > -static void __clear_sched_clock_stable(struct work_struct *work) > +static void __sched_clock_work(struct work_struct *work) > +{ > + static_branch_disable(&__sched_clock_stable); > +} > + > +static DECLARE_WORK(sched_clock_work, __sched_clock_work); > + > +static void __clear_sched_clock_stable(void) > { > struct sched_clock_data *scd = this_scd(); > > @@ -160,11 +167,11 @@ static void __clear_sched_clock_stable(struct work_struct *work) > scd->tick_gtod, gtod_offset, > scd->tick_raw, raw_offset); > > - static_branch_disable(&__sched_clock_stable); > tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); > -} > > -static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable); > + if (sched_clock_stable()) > + schedule_work(&sched_clock_work); > +} > > void clear_sched_clock_stable(void) > { > @@ -173,7 +180,7 @@ void clear_sched_clock_stable(void) > smp_mb(); /* matches sched_clock_init_late() */ > > if (sched_clock_running == 2) > - schedule_work(&sched_clock_work); > + __clear_sched_clock_stable(); > } > > void sched_clock_init_late(void) >