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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 20 Jun 2019 22:20:34 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5KLKXUn23134518 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 20 Jun 2019 21:20:33 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 38B55B2064; Thu, 20 Jun 2019 21:20:33 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1B6C8B205F; Thu, 20 Jun 2019 21:20:33 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 20 Jun 2019 21:20:33 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 1D16816C2A15; Thu, 20 Jun 2019 14:20:35 -0700 (PDT) Date: Thu, 20 Jun 2019 14:20:35 -0700 From: "Paul E. McKenney" To: Scott Wood Cc: Sebastian Andrzej Siewior , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Juri Lelli , Clark Williams , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RT 1/4] rcu: Acquire RCU lock when disabling BHs Reply-To: paulmck@linux.ibm.com References: <20190619011908.25026-1-swood@redhat.com> <20190619011908.25026-2-swood@redhat.com> <20190620205352.GV26519@linux.ibm.com> <1b6dfc95bba69aa53e4e84eebf6af60f0b9ed95c.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1b6dfc95bba69aa53e4e84eebf6af60f0b9ed95c.camel@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19062021-0064-0000-0000-000003F08BF6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011299; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01220870; UDB=6.00642276; IPR=6.01002009; MB=3.00027397; MTD=3.00000008; XFM=3.00000015; UTC=2019-06-20 21:20:37 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19062021-0065-0000-0000-00003DF630BE Message-Id: <20190620212035.GY26519@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-20_14:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906200152 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 20, 2019 at 04:06:02PM -0500, Scott Wood wrote: > On Thu, 2019-06-20 at 13:53 -0700, Paul E. McKenney wrote: > > On Tue, Jun 18, 2019 at 08:19:05PM -0500, Scott Wood wrote: > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > index fb267bc04fdf..aca4e5e25ace 100644 > > > --- a/include/linux/rcupdate.h > > > +++ b/include/linux/rcupdate.h > > > @@ -637,10 +637,12 @@ static inline void rcu_read_unlock(void) > > > static inline void rcu_read_lock_bh(void) > > > { > > > local_bh_disable(); > > > +#ifndef CONFIG_PREEMPT_RT_FULL > > > > How about this instead? > > > > if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL)) > > return; > > OK. > > > > @@ -189,8 +193,10 @@ void __local_bh_enable_ip(unsigned long ip, > > > unsigned int cnt) > > > WARN_ON_ONCE(count < 0); > > > local_irq_enable(); > > > > > > - if (!in_atomic()) > > > + if (!in_atomic()) { > > > + rcu_read_unlock(); > > > local_unlock(bh_lock); > > > + } > > > > > > preempt_check_resched(); > > > } > > > > And I have to ask... > > > > What did you do to test this change to kernel/softirq.c? My past attempts > > to do this sort of thing have always run afoul of open-coded BH > > transitions. > > Mostly rcutorture and loads such as kernel builds, on a debug kernel. By > "open-coded BH transition" do you mean directly manipulating the preempt > count? That would already be broken on RT. OK, then maybe you guys have already done the needed cleanup work. Cool! But don't the additions of rcu_read_lock() and rcu_read_unlock() want to be protected by "!IS_ENABLED(CONFIG_PREEMPT_RT_FULL)" or similar? Thanx, Paul