From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C95FC48BD6 for ; Wed, 26 Jun 2019 16:27:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7268820665 for ; Wed, 26 Jun 2019 16:27:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726368AbfFZQ1L (ORCPT ); Wed, 26 Jun 2019 12:27:11 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:51788 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725958AbfFZQ1K (ORCPT ); Wed, 26 Jun 2019 12:27:10 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5QGMU4S010958; Wed, 26 Jun 2019 12:26:02 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tc9u0y0pv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 26 Jun 2019 12:26:00 -0400 Received: from m0098419.ppops.net (m0098419.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x5QGNWkr013933; Wed, 26 Jun 2019 12:25:59 -0400 Received: from ppma03dal.us.ibm.com (b.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.11]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tc9u0y0p8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 26 Jun 2019 12:25:59 -0400 Received: from pps.filterd (ppma03dal.us.ibm.com [127.0.0.1]) by ppma03dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5QGOmJo001080; Wed, 26 Jun 2019 16:25:58 GMT Received: from b01cxnp22035.gho.pok.ibm.com (b01cxnp22035.gho.pok.ibm.com [9.57.198.25]) by ppma03dal.us.ibm.com with ESMTP id 2t9by78acx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 26 Jun 2019 16:25:58 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5QGPvxZ50200858 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 26 Jun 2019 16:25:58 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E2A54B205F; Wed, 26 Jun 2019 16:25:57 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4E24B2065; Wed, 26 Jun 2019 16:25:57 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 26 Jun 2019 16:25:57 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 0353216C2F90; Wed, 26 Jun 2019 09:25:58 -0700 (PDT) Date: Wed, 26 Jun 2019 09:25:58 -0700 From: "Paul E. McKenney" To: Sebastian Andrzej Siewior Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs Message-ID: <20190626162558.GY26519@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190626135447.y24mvfuid5fifwjc@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190626135447.y24mvfuid5fifwjc@linutronix.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-26_09:,, 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-1906260192 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 26, 2019 at 03:54:47PM +0200, Sebastian Andrzej Siewior wrote: > one of my boxes boots with "threadirqs" and since commit 05f415715ce45 > ("rcu: Speed up expedited GPs when interrupting RCU reader") I run > reliably into the following deadlock: > > | ============================================ > | WARNING: possible recursive locking detected > | 5.2.0-rc6 #279 Not tainted > | -------------------------------------------- > | (cron)/2109 is trying to acquire lock: > | 0000000088464daa (&p->pi_lock){-.-.}, at: try_to_wake_up+0x37/0x700 > | > | but task is already holding lock: > | 0000000088464daa (&p->pi_lock){-.-.}, at: try_to_wake_up+0x37/0x700 > | > | other info that might help us debug this: > | Possible unsafe locking scenario: > | > | CPU0 > | ---- > | lock(&p->pi_lock); > | lock(&p->pi_lock); > | > | *** DEADLOCK *** > | > | May be due to missing lock nesting notation > | > | 4 locks held by (cron)/2109: > | #0: 00000000c0ae63d9 (&sb->s_type->i_mutex_key){++++}, at: iterate_dir+0x3d/0x170 > | #1: 0000000088464daa (&p->pi_lock){-.-.}, at: try_to_wake_up+0x37/0x700 > | #2: 00000000f62f14cf (&rq->lock){-.-.}, at: try_to_wake_up+0x209/0x700 > | #3: 000000000d32568e (rcu_read_lock){....}, at: cpuacct_charge+0x37/0x1e0 > | > | stack backtrace: > | CPU: 3 PID: 2109 Comm: (cron) Not tainted 5.2.0-rc6 #279 > | Call Trace: > | > | dump_stack+0x67/0x90 > | __lock_acquire.cold.63+0x142/0x23a > | lock_acquire+0x9b/0x1a0 > | ? try_to_wake_up+0x37/0x700 > | _raw_spin_lock_irqsave+0x33/0x50 > | ? try_to_wake_up+0x37/0x700 > | try_to_wake_up+0x37/0x700 > wake up ksoftirqd > > | rcu_read_unlock_special+0x61/0xa0 > | __rcu_read_unlock+0x58/0x60 > | cpuacct_charge+0xeb/0x1e0 > | update_curr+0x15d/0x350 > | enqueue_entity+0x115/0x7e0 > | enqueue_task_fair+0x78/0x450 > | activate_task+0x41/0x90 > | ttwu_do_activate+0x49/0x80 > | try_to_wake_up+0x23f/0x700 > > wake up ksoftirqd > > | irq_exit+0xba/0xc0 > | smp_apic_timer_interrupt+0xb2/0x2a0 > | apic_timer_interrupt+0xf/0x20 > | > > based one the commit it seems the problem was always there but now the > mix of raise_softirq_irqoff() and set_tsk_need_resched() seems to hit > the window quite reliably. Replacing it with > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 1102765f91fd1..baab36f4d0f45 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -627,14 +627,7 @@ static void rcu_read_unlock_special(struct task_struct *t) > if (preempt_bh_were_disabled || irqs_were_disabled) { > WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false); > /* Need to defer quiescent state until everything is enabled. */ > - if (irqs_were_disabled) { > - /* Enabling irqs does not reschedule, so... */ > - raise_softirq_irqoff(RCU_SOFTIRQ); > - } else { > - /* Enabling BH or preempt does reschedule, so... */ > - set_tsk_need_resched(current); > - set_preempt_need_resched(); > - } > + raise_softirq_irqoff(RCU_SOFTIRQ); > local_irq_restore(flags); > return; > } > > will make it go away. Color me confused. Neither set_tsk_need_resched() nor set_preempt_need_resched() acquire locks or do wakeups. Yet raise_softirq_irqoff() can do a wakeup if not called from hardirq/softirq/NMI context, so I would instead expect raise_softirq_irqoff() to be the source of troubles when interrupts are threaded. What am I missing here? > Any suggestions? Does something like IRQ work help? Please see -rcu commit 0864f057b050 ("rcu: Use irq_work to get scheduler's attention in clean context") for one way of doing this. Perhaps in combination with -rcu commit a69987a515c8 ("rcu: Simplify rcu_read_unlock_special() deferred wakeups"). Thanx, Paul