linux-kernel - [PATCH 7/9] x86/topology.c: Support functions for BSP online/offline

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Date:	Fri,  4 Nov 2011 15:03:59 -0700
From:	"Fenghua Yu" <fenghua.yu@...el.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>,
	"H Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Tony Luck" <tony.luck@...el.com>,
	"Suresh B Siddha" <suresh.b.siddha@...el.com>,
	"Len Brown" <len.brown@...el.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH 7/9] x86/topology.c: Support functions for BSP online/offline

From: Fenghua Yu <fenghua.yu@...el.com>

By default, BSP can't be hotpluggable because bsp_hotpluggable is 0. Kernel
parameter bsp_hotplug can enable BSP hotplug feature.

arch_cpu_maps_update_begin() and arch_cpu_maps_update_done() locks/unlocks
pm_mutex. This solves cpu maps race condition between BSP online check during
hibernate/suspend and BSP online/offline operations.

arch_state_check() checks if BSP is still the first online CPU.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 arch/x86/kernel/topology.c |   44 +++++++++++++++++++++++++++++++++++++-------
 1 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 8927486..287d7b6 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -29,23 +29,53 @@
 #include <linux/mmzone.h>
 #include <linux/init.h>
 #include <linux/smp.h>
+#include <linux/suspend.h>
 #include <asm/cpu.h>
 
 static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
 
 #ifdef CONFIG_HOTPLUG_CPU
+
+static int bsp_hotpluggable;
+
+static int __init enable_bsp_hotplug(char *str)
+{
+	bsp_hotpluggable = 1;
+	return 0;
+}
+
+__setup("bsp_hotplug", enable_bsp_hotplug);
+
+void arch_cpu_maps_update_begin(void)
+{
+	lock_system_sleep();
+}
+
+void arch_cpu_maps_update_done(void)
+{
+	unlock_system_sleep();
+}
+
+int arch_state_check(void)
+{
+	if (cpumask_first(cpu_online_mask) != 0) {
+		printk(KERN_WARNING "No CPU0.\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
 int __ref arch_register_cpu(int num)
 {
 	/*
-	 * CPU0 cannot be offlined due to several
-	 * restrictions and assumptions in kernel. This basically
-	 * doesn't add a control file, one cannot attempt to offline
-	 * BSP.
+	 * Suspend/resume depends on BSP. PIC interrupts depend on BSP.
 	 *
-	 * Also certain PCI quirks require not to enable hotplug control
-	 * for all CPU's.
+	 * If the BSP depencies are under control, tell kernel to
+	 * enable BSP hotplug. This basically adds a control file and
+	 * one can attempt to offline BSP.
 	 */
-	if (num)
+	if (num || bsp_hotpluggable)
 		per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
 
 	return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
-- 
1.6.0.3

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