From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754533AbeDBWDt (ORCPT ); Mon, 2 Apr 2018 18:03:49 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:47342 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754469AbeDBWDs (ORCPT ); Mon, 2 Apr 2018 18:03:48 -0400 Date: Mon, 2 Apr 2018 15:04:38 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: frederic@kernel.org, cmetcalf@mellanox.com, cl@linux.com, lcapitulino@redhat.com, efault@gmx.de, peterz@infradead.org, riel@redhat.com, tglx@linutronix.de, kernellwp@gmail.com, mingo@kernel.org Subject: NO_HZ_FULL and tick running within a reasonable amount of time Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18040222-0048-0000-0000-0000025438E7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008791; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000255; SDB=6.01012210; UDB=6.00515856; IPR=6.00791477; MB=3.00020380; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-02 22:03:45 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040222-0049-0000-0000-000044A341FE Message-Id: <20180402220438.GA15885@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-04-02_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804020240 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! I am hitting the following on today's mainline under rcutorture, but only on scenarios built with CONFIG_NO_HZ_FULL=y: ------------------------------------------------------------------------ WARNING: CPU: 0 PID: 7 at /home/paulmck/public_git/linux-rcu/kernel/sched/core.c:3124 sched_tick_remote+0x113/0x120 Modules linked in: CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 4.16.0+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 Workqueue: events_unbound sched_tick_remote RIP: 0010:sched_tick_remote+0x113/0x120 RSP: 0018:ffff94d540103e20 EFLAGS: 00010002 RAX: 000000012e9bb357 RBX: ffff8f95dfd21840 RCX: 000000000000001f RDX: 00000000b2d05e00 RSI: 00000000ffffffff RDI: ffff8f95dfd21858 RBP: ffff94d540103e48 R08: 00000000f6499019 R09: 00000000f6499000 R10: 00000000b163d33b R11: ffffffffa5c8c212 R12: ffff8f95dfd25518 R13: ffff8f95de9e4200 R14: 0000000000003402 R15: ffff8f95dfd21858 FS: 0000000000000000(0000) GS:ffff8f95dfc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000a015b40 CR3: 000000001de14000 CR4: 00000000000006f0 Call Trace: process_one_work+0x1d9/0x6a0 worker_thread+0x42/0x420 kthread+0xf3/0x130 ? rescuer_thread+0x340/0x340 ? kthread_delayed_work_timer_fn+0x80/0x80 ret_from_fork+0x3a/0x50 Code: ff 48 8b 83 80 0b 00 00 48 85 c0 0f 85 41 ff ff ff e9 45 ff ff ff be ff ff ff ff 4c 89 ff e8 55 44 02 00 85 c0 75 87 0f 0b eb 83 <0f> 0b eb 97 66 0f 1f 84 00 00 00 00 00 41 57 41 56 41 55 41 54 ---[ end trace fbdcbe529a8ae799 ]-- ------------------------------------------------------------------------ The WARN_ON_ONCE() triggering is this guy: delta = rq_clock_task(rq) - curr->se.exec_start; WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3); But given that ->se.exec_start is zeroed from time to time, for example, in migrate_task_rq_fair(), I am a bit suspicious of this check. What am I missing here? Thanx, Paul