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

From: Fenghua Yu
Date: Fri Nov 04 2011 - 18:21:39 EST


From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

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@xxxxxxxxx>
---
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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