From b9d10be7a8e88fdcb12540387c219cdde87b0795 Mon Sep 17 00:00:00 2001 From: Toshi Kani Date: Mon, 12 Aug 2013 09:45:53 -0600 Subject: 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 Signed-off-by: Rafael J. Wysocki --- include/linux/cpu.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux') diff --git a/include/linux/cpu.h b/include/linux/cpu.h index ab0eade73039..956c0a16566f 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -172,6 +172,8 @@ extern struct bus_type cpu_subsys; #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 @@ static inline void cpu_hotplug_driver_unlock(void) #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) -- cgit v1.2.3