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| author | Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> | 2012-10-23 01:30:54 +0200 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2012-11-15 00:16:00 +0100 |
| commit | 5e5041f3527b36b58e864886ba34c179ad40ff92 (patch) | |
| tree | 16857e196f4d02f89d2934f5a59bc41fa52ef451 /drivers/acpi/processor_driver.c | |
| parent | 73d4511a5f1e208399b2f7a058b73578c1977611 (diff) | |
| download | linux-5e5041f3527b36b58e864886ba34c179ad40ff92.tar.bz2 | |
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.c | 14 |
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 |