From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752046AbdHaHjn (ORCPT ); Thu, 31 Aug 2017 03:39:43 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:58721 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751507AbdHaHbc (ORCPT ); Thu, 31 Aug 2017 03:31:32 -0400 Message-Id: <20170831073053.437818037@linutronix.de> User-Agent: quilt/0.63-1 Date: Thu, 31 Aug 2017 09:16:04 +0200 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Ingo Molnar , Andrew Morton , Borislav Petkov , Sebastian Siewior , Nicholas Piggin , Don Zickus , Chris Metcalf , Ulrich Obergfell Subject: [patch 06/29] lockup_detector: Rework cpu hotplug locking References: <20170831071558.995235362@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=lockup_detector--Rework-cpu-hotplug-locking.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The watchdog proc interface causes extensive recursive locking of the cpu hotplug percpu rwsem, which is deadlock prone. Replace the get/put_online_cpus() pairs with cpu_hotplug_disable()/enable() calls for now. Later patches will remove that requirement completely. Reported-by: Borislav Petkov Signed-off-by: Thomas Gleixner --- kernel/watchdog.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -703,7 +703,7 @@ static int proc_watchdog_common(int whic int err, old, new; int *watchdog_param = (int *)table->data; - get_online_cpus(); + cpu_hotplug_disable(); mutex_lock(&watchdog_proc_mutex); /* @@ -752,7 +752,7 @@ static int proc_watchdog_common(int whic } out: mutex_unlock(&watchdog_proc_mutex); - put_online_cpus(); + cpu_hotplug_enable(); return err; } @@ -794,7 +794,7 @@ int proc_watchdog_thresh(struct ctl_tabl { int err, old, new; - get_online_cpus(); + cpu_hotplug_disable(); mutex_lock(&watchdog_proc_mutex); old = ACCESS_ONCE(watchdog_thresh); @@ -818,7 +818,7 @@ int proc_watchdog_thresh(struct ctl_tabl } out: mutex_unlock(&watchdog_proc_mutex); - put_online_cpus(); + cpu_hotplug_enable(); return err; } @@ -833,7 +833,7 @@ int proc_watchdog_cpumask(struct ctl_tab { int err; - get_online_cpus(); + cpu_hotplug_disable(); mutex_lock(&watchdog_proc_mutex); err = proc_do_large_bitmap(table, write, buffer, lenp, ppos); @@ -856,7 +856,7 @@ int proc_watchdog_cpumask(struct ctl_tab } mutex_unlock(&watchdog_proc_mutex); - put_online_cpus(); + cpu_hotplug_enable(); return err; }