From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932139AbdCHVxT (ORCPT ); Wed, 8 Mar 2017 16:53:19 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54156 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754533AbdCHVxQ (ORCPT ); Wed, 8 Mar 2017 16:53:16 -0500 Date: Wed, 8 Mar 2017 13:53:06 -0800 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@redhat.com, peterz@infradead.org, fweisbec@gmail.com Subject: [PATCH] clock: Fix smp_processor_id() in preemptible bug 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: 17030821-0024-0000-0000-00000200E41B X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006747; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000206; SDB=6.00831871; UDB=6.00408183; IPR=6.00609463; BA=6.00005201; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014564; XFM=3.00000013; UTC=2017-03-08 21:53:08 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17030821-0025-0000-0000-0000425CCBA4 Message-Id: <20170308215306.GA8776@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-08_16:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703080170 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The v4.11-rc1 kernel emits the following splat in some configurations: [ 43.681891] BUG: using smp_processor_id() in preemptible [00000000] code: kworker/3:1/49 [ 43.682511] caller is debug_smp_processor_id+0x17/0x20 [ 43.682893] CPU: 0 PID: 49 Comm: kworker/3:1 Not tainted 4.11.0-rc1+ #1 [ 43.683382] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 [ 43.683497] Workqueue: events __clear_sched_clock_stable [ 43.683497] Call Trace: [ 43.683497] dump_stack+0x4f/0x69 [ 43.683497] check_preemption_disabled+0xd9/0xf0 [ 43.683497] debug_smp_processor_id+0x17/0x20 [ 43.683497] __clear_sched_clock_stable+0x11/0x60 [ 43.683497] process_one_work+0x146/0x430 [ 43.683497] worker_thread+0x126/0x490 [ 43.683497] kthread+0xfc/0x130 [ 43.683497] ? process_one_work+0x430/0x430 [ 43.683497] ? kthread_create_on_node+0x40/0x40 [ 43.683497] ? umh_complete+0x30/0x30 [ 43.683497] ? call_usermodehelper_exec_async+0x12a/0x130 [ 43.683497] ret_from_fork+0x29/0x40 [ 43.689244] sched_clock: Marking unstable (43688244724, 179505618)<-(43867750342, 0) This happens because workqueue handlers run with preemption enabled by default and the new this_scd() function accesses per-CPU variables. This commit therefore disables preemption across this call to this_scd() and to the uses of the pointer that it returns. Lightly tested successfully on x86. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Frederic Weisbecker diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index a08795e21628..aa184bea1344 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -143,7 +143,7 @@ static void __set_sched_clock_stable(void) static void __clear_sched_clock_stable(struct work_struct *work) { - struct sched_clock_data *scd = this_scd(); + struct sched_clock_data *scd; /* * Attempt to make the stable->unstable transition continuous. @@ -154,7 +154,10 @@ static void __clear_sched_clock_stable(struct work_struct *work) * * Still do what we can. */ + preempt_disable(); + scd = this_scd(); gtod_offset = (scd->tick_raw + raw_offset) - (scd->tick_gtod); + preempt_enable(); printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", scd->tick_gtod, gtod_offset,