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>

1 files changed, 16 insertions, 5 deletions

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 5a74a9c1e42c..f29e06efa479 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -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));