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authorYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>2012-10-23 01:30:54 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2012-11-15 00:16:00 +0100
commit5e5041f3527b36b58e864886ba34c179ad40ff92 (patch)
tree16857e196f4d02f89d2934f5a59bc41fa52ef451 /kernel/cpu.c
parent73d4511a5f1e208399b2f7a058b73578c1977611 (diff)
ACPI / processor: prevent cpu from becoming online
Even if acpi_processor_handle_eject() offlines cpu, there is a chance to online the cpu after that. So the patch closes the window by using get/put_online_cpus(). Why does the patch change _cpu_up() logic? The patch cares the race of hot-remove cpu and _cpu_up(). If the patch does not change it, there is the following race. hot-remove cpu | _cpu_up() ------------------------------------- ------------------------------------ call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | call put_online_cpus() | | start and continue _cpu_up() return acpi_processor_remove() | continue hot-remove the cpu | So _cpu_up() can continue to itself. And hot-remove cpu can also continue itself. If the patch changes _cpu_up() logic, the race disappears as below: hot-remove cpu | _cpu_up() ----------------------------------------------------------------------- call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | cpu's cpu_present is set | to false by set_cpu_present()| call put_online_cpus() | | start _cpu_up() | check cpu_present() and return -EINVAL return acpi_processor_remove() | continue hot-remove the cpu | Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Toshi Kani <toshi.kani@hp.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 42bd331ee0ab..f45657f1eb8e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -348,11 +348,13 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
struct task_struct *idle;
- if (cpu_online(cpu) || !cpu_present(cpu))
- return -EINVAL;
-
cpu_hotplug_begin();
+ if (cpu_online(cpu) || !cpu_present(cpu)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
idle = idle_thread_get(cpu);
if (IS_ERR(idle)) {
ret = PTR_ERR(idle);

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