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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: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Toshi Kani 2013-08-12 09:45:53 -06:00 committed by Rafael J. Wysocki
parent 22e7551eb6
commit b9d10be7a8
3 changed files with 23 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/acpi/acpi_processor.c
View File

@ -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));

4
include/linux/cpu.h
View File

@ -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)

9
kernel/cpu.c
View File

@ -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)