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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 EA267C3A5A0 for ; Wed, 21 Aug 2019 23:19:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C060C2339E for ; Wed, 21 Aug 2019 23:19:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731418AbfHUXTP (ORCPT ); Wed, 21 Aug 2019 19:19:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43376 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731413AbfHUXTO (ORCPT ); Wed, 21 Aug 2019 19:19:14 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 09C307FDCD; Wed, 21 Aug 2019 23:19:14 +0000 (UTC) Received: from t460p.redhat.com (ovpn-117-150.phx2.redhat.com [10.3.117.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id CB317600CD; Wed, 21 Aug 2019 23:19:12 +0000 (UTC) From: Scott Wood To: Sebastian Andrzej Siewior Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, "Paul E . McKenney" , Joel Fernandes , Thomas Gleixner , Peter Zijlstra , Juri Lelli , Clark Williams , Scott Wood Subject: [PATCH RT v2 3/3] rcu: Disable use_softirq on PREEMPT_RT Date: Wed, 21 Aug 2019 18:19:06 -0500 Message-Id: <20190821231906.4224-4-swood@redhat.com> In-Reply-To: <20190821231906.4224-1-swood@redhat.com> References: <20190821231906.4224-1-swood@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 21 Aug 2019 23:19:14 +0000 (UTC) Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org Besides restoring behavior that used to be default on RT, this avoids a deadlock on scheduler locks: [ 136.894657] 039: ============================================ [ 136.900401] 039: WARNING: possible recursive locking detected [ 136.906146] 039: 5.2.9-rt3.dbg+ #174 Tainted: G E [ 136.912152] 039: -------------------------------------------- [ 136.917896] 039: rcu_torture_rea/13474 is trying to acquire lock: [ 136.923990] 039: 000000005f25146d [ 136.927310] 039: ( [ 136.929414] 039: &p->pi_lock [ 136.932303] 039: ){-...} [ 136.934840] 039: , at: try_to_wake_up+0x39/0x920 [ 136.939461] 039: but task is already holding lock: [ 136.944425] 039: 000000005f25146d [ 136.947745] 039: ( [ 136.949852] 039: &p->pi_lock [ 136.952738] 039: ){-...} [ 136.955274] 039: , at: try_to_wake_up+0x39/0x920 [ 136.959895] 039: other info that might help us debug this: [ 136.965555] 039: Possible unsafe locking scenario: [ 136.970608] 039: CPU0 [ 136.973493] 039: ---- [ 136.976378] 039: lock( [ 136.978918] 039: &p->pi_lock [ 136.981806] 039: ); [ 136.983911] 039: lock( [ 136.986451] 039: &p->pi_lock [ 136.989336] 039: ); [ 136.991444] 039: *** DEADLOCK *** [ 136.995194] 039: May be due to missing lock nesting notation [ 137.001115] 039: 3 locks held by rcu_torture_rea/13474: [ 137.006341] 039: #0: [ 137.008707] 039: 000000005f25146d [ 137.012024] 039: ( [ 137.014131] 039: &p->pi_lock [ 137.017015] 039: ){-...} [ 137.019558] 039: , at: try_to_wake_up+0x39/0x920 [ 137.024175] 039: #1: [ 137.026540] 039: 0000000011c8e51d [ 137.029859] 039: ( [ 137.031966] 039: &rq->lock [ 137.034679] 039: ){-...} [ 137.037217] 039: , at: try_to_wake_up+0x241/0x920 [ 137.041924] 039: #2: [ 137.044291] 039: 00000000098649b9 [ 137.047610] 039: ( [ 137.049714] 039: rcu_read_lock [ 137.052774] 039: ){....} [ 137.055314] 039: , at: cpuacct_charge+0x33/0x1e0 [ 137.059934] 039: stack backtrace: [ 137.063425] 039: CPU: 39 PID: 13474 Comm: rcu_torture_rea Kdump: loaded Tainted: G E 5.2.9-rt3.dbg+ #174 [ 137.074197] 039: Hardware name: Intel Corporation S2600BT/S2600BT, BIOS SE5C620.86B.01.00.0763.022420181017 02/24/2018 [ 137.084886] 039: Call Trace: [ 137.087773] 039: [ 137.090226] 039: dump_stack+0x5e/0x8b [ 137.093997] 039: __lock_acquire+0x725/0x1100 [ 137.098358] 039: lock_acquire+0xc0/0x240 [ 137.102374] 039: ? try_to_wake_up+0x39/0x920 [ 137.106737] 039: _raw_spin_lock_irqsave+0x47/0x90 [ 137.111534] 039: ? try_to_wake_up+0x39/0x920 [ 137.115910] 039: try_to_wake_up+0x39/0x920 [ 137.120098] 039: rcu_read_unlock_special+0x65/0xb0 [ 137.124977] 039: __rcu_read_unlock+0x5d/0x70 [ 137.129337] 039: cpuacct_charge+0xd9/0x1e0 [ 137.133522] 039: ? cpuacct_charge+0x33/0x1e0 [ 137.137880] 039: update_curr+0x14b/0x420 [ 137.141894] 039: enqueue_entity+0x42/0x370 [ 137.146080] 039: enqueue_task_fair+0xa9/0x490 [ 137.150528] 039: activate_task+0x5a/0xf0 [ 137.154539] 039: ttwu_do_activate+0x4e/0x90 [ 137.158813] 039: try_to_wake_up+0x277/0x920 [ 137.163086] 039: irq_exit+0xb6/0xf0 [ 137.166661] 039: smp_apic_timer_interrupt+0xe3/0x3a0 [ 137.171714] 039: apic_timer_interrupt+0xf/0x20 [ 137.176249] 039: [ 137.178785] 039: RIP: 0010:__schedule+0x0/0x8e0 [ 137.183319] 039: Code: 00 02 48 89 43 20 e8 0f 5a 00 00 48 8d 7b 28 e8 86 f2 fd ff 31 c0 5b 5d 41 5c c3 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <55> 48 89 e5 41 57 41 56 49 c7 c6 c0 ca 1e 00 41 55 41 89 fd 41 54 [ 137.202498] 039: RSP: 0018:ffffc9005835fbc0 EFLAGS: 00000246 [ 137.208158] 039: ORIG_RAX: ffffffffffffff13 [ 137.212428] 039: RAX: 0000000000000000 RBX: ffff8897c3e1bb00 RCX: 0000000000000001 [ 137.219994] 039: RDX: 0000000080004008 RSI: 0000000000000006 RDI: 0000000000000001 [ 137.227560] 039: RBP: ffff8897c3e1bb00 R08: 0000000000000000 R09: 0000000000000000 [ 137.235126] 039: R10: 0000000000000001 R11: 0000000000000001 R12: ffffffff81001fd1 [ 137.242694] 039: R13: 0000000000000044 R14: 0000000000000000 R15: ffffc9005835fcac [ 137.250259] 039: ? ___preempt_schedule+0x16/0x18 [ 137.254969] 039: preempt_schedule_common+0x32/0x80 [ 137.259846] 039: ___preempt_schedule+0x16/0x18 [ 137.264379] 039: rcutorture_one_extend+0x33a/0x510 [rcutorture] [ 137.270397] 039: rcu_torture_one_read+0x18c/0x450 [rcutorture] [ 137.276334] 039: rcu_torture_reader+0xac/0x1f0 [rcutorture] [ 137.281998] 039: ? rcu_torture_reader+0x1f0/0x1f0 [rcutorture] [ 137.287920] 039: kthread+0x106/0x140 [ 137.291591] 039: ? rcu_torture_one_read+0x450/0x450 [rcutorture] [ 137.297681] 039: ? kthread_bind+0x10/0x10 [ 137.301783] 039: ret_from_fork+0x3a/0x50 Signed-off-by: Scott Wood --- I think the prohibition on use_softirq can be dropped once RT gets the latest RCU code, but the question of what use_softirq should default to on PREEMPT_RT remains. --- kernel/rcu/tree.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index fc8b00c61b32..12036d33e2f9 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -98,9 +98,16 @@ struct rcu_state rcu_state = { /* Dump rcu_node combining tree at boot to verify correct setup. */ static bool dump_tree; module_param(dump_tree, bool, 0444); -/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */ +/* + * By default, use RCU_SOFTIRQ instead of rcuc kthreads. + * But, avoid RCU_SOFTIRQ on PREEMPT_RT due to pi/rq deadlocks. + */ +#ifdef CONFIG_PREEMPT_RT_FULL +static bool use_softirq; +#else static bool use_softirq = 1; module_param(use_softirq, bool, 0444); +#endif /* Control rcu_node-tree auto-balancing at boot time. */ static bool rcu_fanout_exact; module_param(rcu_fanout_exact, bool, 0444); -- 1.8.3.1