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authorYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>2012-10-23 03:30:54 +0400
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2012-11-15 03:16:00 +0400
commit5e5041f3527b36b58e864886ba34c179ad40ff92 (patch)
tree16857e196f4d02f89d2934f5a59bc41fa52ef451 /drivers/acpi/processor_driver.c
parent73d4511a5f1e208399b2f7a058b73578c1977611 (diff)
downloadlinux-5e5041f3527b36b58e864886ba34c179ad40ff92.tar.xz
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 'drivers/acpi/processor_driver.c')
-rw-r--r--drivers/acpi/processor_driver.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index bd4e5dca3ff7..a4352b88a331 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -852,8 +852,22 @@ static int acpi_processor_handle_eject(struct acpi_processor *pr)
if (cpu_online(pr->id))
cpu_down(pr->id);
+ get_online_cpus();
+ /*
+ * The cpu might become online again at this point. So we check whether
+ * the cpu has been onlined or not. If the cpu became online, it means
+ * that someone wants to use the cpu. So acpi_processor_handle_eject()
+ * returns -EAGAIN.
+ */
+ if (unlikely(cpu_online(pr->id))) {
+ put_online_cpus();
+ pr_warn("Failed to remove CPU %d, because other task "
+ "brought the CPU back online\n", pr->id);
+ return -EAGAIN;
+ }
arch_unregister_cpu(pr->id);
acpi_unmap_lsapic(pr->id);
+ put_online_cpus();
return (0);
}
#else