acpi : cpu hot-remove returns error when cpu_down() fails

Even if acpi_processor_handle_eject() offlines cpu, there is a chance to online the cpu after that. So the patch closes the window by using get/put_online_cpus().

Why does the patch change _cpu_up() logic?

The patch cares the race of hot-remove cpu and _cpu_up(). If the patch does not change it, there is the following race.

hot-remove cpu | _cpu_up()
------------------------------------- ------------------------------------

call acpi_processor_handle_eject()     |
     call cpu_down()                   |
     call get_online_cpus()            |
                                       | call cpu_hotplug_begin() and stop here
     call arch_unregister_cpu()        |
     call acpi_unmap_lsapic()          |
     call put_online_cpus()            |
                                       | start and continue _cpu_up()
     return acpi_processor_remove()    |
continue hot-remove the cpu            |

So _cpu_up() can continue to itself. And hot-remove cpu can also continue itself. If the patch changes _cpu_up() logic, the race disappears as below:

hot-remove cpu | _cpu_up()
-----------------------------------------------------------------------

call acpi_processor_handle_eject()     |
     call cpu_down()                   |
     call get_online_cpus()            |
                                       | call cpu_hotplug_begin() and stop here
     call arch_unregister_cpu()        |
     call acpi_unmap_lsapic()          |
          cpu's cpu_present is set     |
          to false by set_cpu_present()|
     call put_online_cpus()            |
                                       | start _cpu_up()
                                       | check cpu_present() and return -EINVAL
     return acpi_processor_remove()    |
continue hot-remove the cpu            |

Reviewed-by Srivatsa S. Bhat <[email protected]>

Signed-off-by Yasuaki Ishimatsu <[email protected]>

---
 drivers/acpi/processor_driver.c |   14 ++++++++++++++
 kernel/cpu.c                    |    8 +++++---
 2 files changed, 19 insertions(+), 3 deletions(-)

Index: linux-3.5-rc6/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +1 -0

@@ -850,8 +850,22 @@ static int acpi_processor_handle_eject(s
 			return ret;
 	}
 
+	get_online_cpus();

drivers/acpi/processor_driver.c +3 -0

+		return -EAGAIN;
+	}
 	arch_unregister_cpu(pr->id);
 	acpi_unmap_lsapic(pr->id);
+	put_online_cpus();
 	return ret;
 }
 #else

Index: linux-3.5-rc6/kernel/cpu.c
===================================================================

kernel/cpu.c +5 -3

@@ -343,11 +343,13 @@ static int __cpuinit _cpu_up(unsigned in
 	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 	struct task_struct *idle;
 
-	if (cpu_online(cpu) || !cpu_present(cpu))
-		return -EINVAL;
-
 	cpu_hotplug_begin();
 
+	if (cpu_online(cpu) || !cpu_present(cpu)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	idle = idle_thread_get(cpu);
 	if (IS_ERR(idle)) {
 		ret = PTR_ERR(idle);

acpi_bus_trim() stops removing devices, when acpi_bus_remove() return error number. But acpi_bus_remove() cannot return error number correctly. acpi_bus_remove() only return -EINVAL, when dev argument is NULL. Thus even if device cannot be removed correctly, acpi_bus_trim() ignores and continues to remove devices. acpi_bus_hot_remove_device() uses acpi_bus_trim() for removing devices. Therefore acpi_bus_hot_remove_device() can send "_EJ0" to firmware, even if the device is running on the system. In this case, the system cannot work well. So acpi_bus_trim() should check whether device was removed or not correctly. The patch adds error check into some functions to remove the device.

device_release_driver() can return error value by the patch. But the change does not impact other caller function excluding acpi_bus_trim(), since all of them does not check return value of device_releae_driver().

Signed-off-by Yasuaki Ishimatsu <[email protected]>

---
 drivers/acpi/scan.c    |   15 ++++++++++++---
 drivers/base/dd.c      |   22 +++++++++++++++++-----
 include/linux/device.h |    2 +-
 3 files changed, 30 insertions(+), 9 deletions(-)

Index: linux-3.5-rc6/drivers/acpi/scan.c
===================================================================

drivers/acpi/scan.c +12 -3

@@ -425,12 +425,17 @@ static int acpi_device_remove(struct dev
 {
 	struct acpi_device *acpi_dev = to_acpi_device(dev);
 	struct acpi_driver *acpi_drv = acpi_dev->driver;
+	int ret;
 
 	if (acpi_drv) {
 		if (acpi_drv->ops.notify)
 			acpi_device_remove_notify_handler(acpi_dev);
-		if (acpi_drv->ops.remove)
-			acpi_drv->ops.remove(acpi_dev, acpi_dev->removal_type);
+		if (acpi_drv->ops.remove) {
+			ret = acpi_drv->ops.remove(acpi_dev,
+						   acpi_dev->removal_type);
+			if (ret)
+				return ret;
+		}
 	}
 	acpi_dev->driver = NULL;
 	acpi_dev->driver_data = NULL;

@@ -1208,11 +1213,15 @@ static int acpi_device_set_context(struc
 
 static int acpi_bus_remove(struct acpi_device *dev, int rmdevice)
 {
+	int ret;
+
 	if (!dev)
 		return -EINVAL;
 
 	dev->removal_type = ACPI_BUS_REMOVAL_EJECT;
-	device_release_driver(&dev->dev);
+	ret = device_release_driver(&dev->dev);
+	if (ret)
+		return ret;
 
 	if (!rmdevice)
 		return 0;

Index: linux-3.5-rc6/drivers/base/dd.c
===================================================================

drivers/base/dd.c +17 -5

@@ -464,9 +464,10 @@ EXPORT_SYMBOL_GPL(driver_attach);
  * __device_release_driver() must be called with @dev lock held.
  * When called for a USB interface, @dev->parent lock must be held as well.
  */
-static void __device_release_driver(struct device *dev)
+static int __device_release_driver(struct device *dev)
 {
 	struct device_driver *drv;
+	int ret = 0;
 
 	drv = dev->driver;
 	if (drv) {

@@ -482,9 +483,11 @@ static void __device_release_driver(stru
 		pm_runtime_put_sync(dev);
 
 		if (dev->bus && dev->bus->remove)
-			dev->bus->remove(dev);
+			ret = dev->bus->remove(dev);
 		else if (drv->remove)
-			drv->remove(dev);
+			ret = drv->remove(dev);
+		if (ret)
+			goto rollback;
 		devres_release_all(dev);
 		dev->driver = NULL;
 		klist_remove(&dev->p->knode_driver);

@@ -494,6 +497,12 @@ static void __device_release_driver(stru
 						     dev);
 
 	}
+
+	return ret;
+
+rollback:
+	driver_sysfs_add(dev);
+	return ret;
 }
 
 /**

@@ -503,16 +512,19 @@ static void __device_release_driver(stru
  * Manually detach device from driver.
  * When called for a USB interface, @dev->parent lock must be held.
  */
-void device_release_driver(struct device *dev)
+int device_release_driver(struct device *dev)
 {
+	int ret;
 	/*
 	 * If anyone calls device_release_driver() recursively from
 	 * within their ->remove callback for the same device, they
 	 * will deadlock right here.
 	 */
 	device_lock(dev);
-	__device_release_driver(dev);
+	ret = __device_release_driver(dev);
 	device_unlock(dev);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(device_release_driver);
 

Index: linux-3.5-rc6/include/linux/device.h
===================================================================

include/linux/device.h +1 -1

@@ -827,7 +827,7 @@ static inline void *dev_get_platdata(con
  * for information on use.
  */
 extern int __must_check device_bind_driver(struct device *dev);
-extern void device_release_driver(struct device *dev);
+extern int device_release_driver(struct device *dev);
 extern int  __must_check device_attach(struct device *dev);
 extern int __must_check driver_attach(struct device_driver *drv);
 extern int __must_check device_reprobe(struct device *dev);

Even if cpu_down() fails, acpi_processor_remove() continues to remove the cpu. But in this case, it should return error number since some process may run on the cpu. If the cpu has a running process and the cpu is turned the power off, the system may not work well.

Reviewed-by Srivatsa S. Bhat <[email protected]>

Signed-off-by Yasuaki Ishimatsu <[email protected]>

---
 drivers/acpi/processor_driver.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

Index: linux-3.5-rc6/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +12 -6

@@ -610,7 +610,7 @@ err_free_pr:
 static int acpi_processor_remove(struct acpi_device *device, int type)
 {
 	struct acpi_processor *pr = NULL;
-
+	int ret;
 
 	if (!device || !acpi_driver_data(device))
 		return -EINVAL;

@@ -621,8 +621,9 @@ static int acpi_processor_remove(struct
 		goto free;
 
 	if (type == ACPI_BUS_REMOVAL_EJECT) {
-		if (acpi_processor_handle_eject(pr))
-			return -EINVAL;
+		ret = acpi_processor_handle_eject(pr);
+		if (ret)
+			return ret;
 	}
 
 	acpi_processor_power_exit(pr, device);

@@ -841,12 +842,17 @@ static acpi_status acpi_processor_hotadd
 
 static int acpi_processor_handle_eject(struct acpi_processor *pr)
 {
-	if (cpu_online(pr->id))
-		cpu_down(pr->id);
+	int ret = 0;
+
+	if (cpu_online(pr->id)) {
+		ret = cpu_down(pr->id);
+		if (ret)
+			return ret;
+	}
 
 	arch_unregister_cpu(pr->id);
 	acpi_unmap_lsapic(pr->id);
-	return (0);
+	return ret;
 }
 #else
 static acpi_status acpi_processor_hotadd_init(struct acpi_processor *pr)