ACPI / processor: Acquire writer lock to update CPU maps
CPU system maps are protected with reader/writer locks. The reader
lock, get_online_cpus(), assures that the maps are not updated while
holding the lock. The writer lock, cpu_hotplug_begin(), is used to
udpate the cpu maps along with cpu_maps_update_begin().
However, the ACPI processor handler updates the cpu maps without
holding the the writer lock.
acpi_map_lsapic() is called from acpi_processor_hotadd_init() to
update cpu_possible_mask and cpu_present_mask. acpi_unmap_lsapic()
is called from acpi_processor_remove() to update cpu_possible_mask.
Currently, they are either unprotected or protected with the reader
lock, which is not correct.
For example, the get_online_cpus() below is supposed to assure that
cpu_possible_mask is not changed while the code is iterating with
for_each_possible_cpu().
get_online_cpus();
for_each_possible_cpu(cpu) {
:
}
put_online_cpus();
However, this lock has no protection with CPU hotplug since the ACPI
processor handler does not use the writer lock when it updates
cpu_possible_mask. The reader lock does not serialize within the
readers.
This patch protects them with the writer lock with cpu_hotplug_begin()
along with cpu_maps_update_begin(), which must be held before calling
cpu_hotplug_begin(). It also protects arch_register_cpu() /
arch_unregister_cpu(), which creates / deletes a sysfs cpu device
interface. For this purpose it changes cpu_hotplug_begin() and
cpu_hotplug_done() to global and exports them in cpu.h.
Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index ab0eade..956c0a1 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -172,6 +172,8 @@
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */
+extern void cpu_hotplug_begin(void);
+extern void cpu_hotplug_done(void);
extern void get_online_cpus(void);
extern void put_online_cpus(void);
extern void cpu_hotplug_disable(void);
@@ -197,6 +199,8 @@
#else /* CONFIG_HOTPLUG_CPU */
+static inline void cpu_hotplug_begin(void) {}
+static inline void cpu_hotplug_done(void) {}
#define get_online_cpus() do { } while (0)
#define put_online_cpus() do { } while (0)
#define cpu_hotplug_disable() do { } while (0)