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Commit b9d10be7 authored by Toshi Kani's avatar Toshi Kani Committed by Rafael J. Wysocki
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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: default avatarToshi Kani <toshi.kani@hp.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 22e7551e

drivers/acpi/acpi_processor.c

+16 −5
Original line number Diff line number Diff line
@@ -178,14 +178,17 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr) 
	if (ACPI_FAILURE(status) || !(sta & ACPI_STA_DEVICE_PRESENT))

		return -ENODEV;



	cpu_maps_update_begin();

	cpu_hotplug_begin();



	ret = acpi_map_lsapic(pr->handle, &pr->id);

	if (ret)

		return ret;

		goto out;



	ret = arch_register_cpu(pr->id);

	if (ret) {

		acpi_unmap_lsapic(pr->id);

		return ret;

		goto out;

	}



	/*
@@ -195,7 +198,11 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr) 
	 */

	pr_info("CPU%d has been hot-added\n", pr->id);

	pr->flags.need_hotplug_init = 1;

	return 0;



out:

	cpu_hotplug_done();

	cpu_maps_update_done();

	return ret;

}

#else

static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
@@ -452,11 +459,15 @@ static void acpi_processor_remove(struct acpi_device *device) 
	per_cpu(processor_device_array, pr->id) = NULL;

	per_cpu(processors, pr->id) = NULL;



	cpu_maps_update_begin();

	cpu_hotplug_begin();



	/* Remove the CPU. */

	get_online_cpus();

	arch_unregister_cpu(pr->id);

	acpi_unmap_lsapic(pr->id);

	put_online_cpus();



	cpu_hotplug_done();

	cpu_maps_update_done();



	try_offline_node(cpu_to_node(pr->id));

include/linux/cpu.h

+4 −0
Original line number Diff line number Diff line
@@ -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)

kernel/cpu.c

+3 −6
Original line number Diff line number Diff line
@@ -113,7 +113,7 @@ EXPORT_SYMBOL_GPL(put_online_cpus); 
 * get_online_cpus() not an api which is called all that often.

 *

 */

static void cpu_hotplug_begin(void)

void cpu_hotplug_begin(void)

{

	cpu_hotplug.active_writer = current;
@@ -127,7 +127,7 @@ static void cpu_hotplug_begin(void) 
	}

}



static void cpu_hotplug_done(void)

void cpu_hotplug_done(void)

{

	cpu_hotplug.active_writer = NULL;

	mutex_unlock(&cpu_hotplug.lock);
@@ -154,10 +154,7 @@ void cpu_hotplug_enable(void) 
	cpu_maps_update_done();

}



#else /* #if CONFIG_HOTPLUG_CPU */

static void cpu_hotplug_begin(void) {}

static void cpu_hotplug_done(void) {}

#endif	/* #else #if CONFIG_HOTPLUG_CPU */

#endif	/* CONFIG_HOTPLUG_CPU */



/* Need to know about CPUs going up/down? */

int __ref register_cpu_notifier(struct notifier_block *nb)