From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932606AbdCIPZT (ORCPT ); Thu, 9 Mar 2017 10:25:19 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:42686 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754766AbdCIPZP (ORCPT ); Thu, 9 Mar 2017 10:25:15 -0500 Date: Thu, 9 Mar 2017 16:24:20 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, fweisbec@gmail.com Subject: Re: [PATCH] clock: Fix smp_processor_id() in preemptible bug Message-ID: <20170309152420.GC3343@twins.programming.kicks-ass.net> References: <20170308215306.GA8776@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170308215306.GA8776@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 08, 2017 at 01:53:06PM -0800, Paul E. McKenney wrote: > 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. Does this also work? --- kernel/sched/clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index a08795e21628..c63042253b65 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -173,7 +173,7 @@ void clear_sched_clock_stable(void) smp_mb(); /* matches sched_clock_init_late() */ if (sched_clock_running == 2) - schedule_work(&sched_clock_work); + schedule_work_on(smp_processor_id(), &sched_clock_work); } void sched_clock_init_late(void)