From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758725AbdELSgP (ORCPT ); Fri, 12 May 2017 14:36:15 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:39736 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756524AbdELSgO (ORCPT ); Fri, 12 May 2017 14:36:14 -0400 Date: Fri, 12 May 2017 11:35:59 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Mathieu Desnoyers , Masami Hiramatsu Subject: Re: [RFC][PATCH 2/5] cpu-hotplug: Allow get_online_cpus() to nest Reply-To: paulmck@linux.vnet.ibm.com References: <20170512171544.100715273@goodmis.org> <20170512172450.000006488@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170512172450.000006488@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17051218-0040-0000-0000-0000033B41D5 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007051; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000211; SDB=6.00859621; UDB=6.00426126; IPR=6.00639204; BA=6.00005345; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015431; XFM=3.00000015; UTC=2017-05-12 18:36:11 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17051218-0041-0000-0000-0000072F6BE5 Message-Id: <20170512183559.GA3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-12_10:,, 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=8.0.1-1703280000 definitions=main-1705120346 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 12, 2017 at 01:15:46PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" > > Allow get_online_cpus() to be recursive. If a lock is taken while under > "get_online_cpus()", it can call get_online_cpus() as well, just as long as > it is never held without being under get_online_cpus(), but then calling it. > > GOC() -> Lock(X) -> GOC() > > is OK, as long as > > Lock(X) -> GOC() > > does not exist. > > Signed-off-by: Steven Rostedt (VMware) Does ->goc_depth also need to be initialized in include/linux/init_task.h? It seems like C-language initialization-to-zero would cover this, but there is a lot of initialization to zero values in init_task.h (including but not limited to some RCU stuff). Other than that, this does look like it might ease use of get_online_cpus() in combination with CPU-hotplug notifiers, although it would not have made any difference in any of the RCU use cases. Thanx, Paul > --- > include/linux/sched.h | 1 + > kernel/cpu.c | 9 +++++++++ > kernel/fork.c | 1 + > 3 files changed, 11 insertions(+) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 993e7e25a3a5..8f272ab57685 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -813,6 +813,7 @@ struct task_struct { > unsigned int lockdep_recursion; > struct held_lock held_locks[MAX_LOCK_DEPTH]; > gfp_t lockdep_reclaim_gfp; > + int goc_depth; > #endif > > #ifdef CONFIG_UBSAN > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 983163ef36ee..0dbdf1e69715 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -209,12 +209,21 @@ DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock); > > void get_online_cpus(void) > { > +#ifdef CONFIG_LOCKDEP > + if (current->goc_depth++) > + return; > +#endif > percpu_down_read(&cpu_hotplug_lock); > } > EXPORT_SYMBOL_GPL(get_online_cpus); > > void put_online_cpus(void) > { > +#ifdef CONFIG_LOCKDEP > + WARN_ON_ONCE(current->goc_depth < 1); > + if (--current->goc_depth) > + return; > +#endif > percpu_up_read(&cpu_hotplug_lock); > } > EXPORT_SYMBOL_GPL(put_online_cpus); > diff --git a/kernel/fork.c b/kernel/fork.c > index dd5a371c392a..8aedcd011ccc 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1658,6 +1658,7 @@ static __latent_entropy struct task_struct *copy_process( > p->lockdep_depth = 0; /* no locks held yet */ > p->curr_chain_key = 0; > p->lockdep_recursion = 0; > + p->goc_depth = 0; > #endif > > #ifdef CONFIG_DEBUG_MUTEXES > -- > 2.10.2 > >