[RFC PATCH v3 22/28] ACPIHP/processor: protect accesses to device->driver_data

[Jiang Liu <liuj97@gmail.com>]

CPU hotplug notification handler acpi_cpu_soft_notify() and driver
unbind method acpi_processor_remove() may be concurrently called.
acpi_cpu_soft_notify() will access device->driver_data, but that
data structure may be destroyed by acpi_processor_remove().

On the other hand, acpi_cpu_soft_notify() is always called under
protection of get_online_cpus(), so use get_online_cpus() to serialize
all accesses and modifications to device->driver_data.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
---
 drivers/acpi/processor_driver.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index 4f2fec0..110c5ac 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -616,6 +616,8 @@ static int __cpuinit acpi_processor_add(struct acpi_device *device)
 		return 0;
 	BUG_ON((pr->id >= nr_cpu_ids) || (pr->id < 0));
 
+	/* block CPU online/offline operations */
+	get_online_cpus();
 	result = acpi_processor_link(device, pr);
 	if (result)
 		goto err_unlock;
@@ -624,6 +626,7 @@ static int __cpuinit acpi_processor_add(struct acpi_device *device)
 		if (result)
 			goto err_unlink;
 	}
+	put_online_cpus();
 
 	return 0;
 
@@ -654,8 +657,10 @@ static int acpi_processor_remove(struct acpi_device *device, int type)
 			return -EINVAL;
 	}
 
-	acpi_processor_stop(device, pr);
+	get_online_cpus();
+	acpi_processor_stop(pr);
 	acpi_processor_unlink(device, pr);
+	put_online_cpus();
 
 free:
 	device->driver_data = NULL;
-- 
1.7.9.5