linux-kernel - Re: ACPI/cpu hotplug: possible lockdep

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Date:	Wed, 30 Jul 2014 15:12:49 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	rafael.j.wysocki@...el.com, Tejun Heo <tj@...nel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: ACPI/cpu hotplug: possible lockdep

On Wednesday, July 30, 2014 02:10:35 PM Gu Zheng wrote:
> Hi Rafael,

Hi,

> A lockdep warning occurs when hot removing a cpu via sysfs:
> echo 1 > /sys/bus/acpi/devices/LNXCPU\:02/eject
> The kernel is latest upstream, and the test box is a kvm vm,
> detail info as following.

Well, I have a theory.

Is the splat still reproducible with the patch below applied?

Rafael

---
 kernel/smp.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-pm/kernel/smp.c
===================================================================
--- linux-pm.orig/kernel/smp.c
+++ linux-pm/kernel/smp.c
@@ -542,6 +542,7 @@ void __init smp_init(void)
 
 	idle_threads_init();
 
+	lock_device_hotplug();
 	/* FIXME: This should be done in userspace --RR */
 	for_each_present_cpu(cpu) {
 		if (num_online_cpus() >= setup_max_cpus)
@@ -549,6 +550,7 @@ void __init smp_init(void)
 		if (!cpu_online(cpu))
 			cpu_up(cpu);
 	}
+	unlock_device_hotplug();
 
 	/* Any cleanup work */
 	smp_announce();

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