linux-next/Documentation/fault-injection/notifier-error-inject.txt

Notifier error injection
========================

Notifier error injection provides the ability to inject artificial errors to
specified notifier chain callbacks. It is useful to test the error handling of
notifier call chain failures which is rarely executed.  There are kernel
modules that can be used to test the following notifiers.

 * CPU notifier
 * PM notifier
 * Memory hotplug notifier
 * powerpc pSeries reconfig notifier

CPU notifier error injection module
-----------------------------------
This feature can be used to test the error handling of the CPU notifiers by
injecting artificial errors to CPU notifier chain callbacks.

If the notifier call chain should be failed with some events notified, write
the error code to debugfs interface
/sys/kernel/debug/notifier-error-inject/cpu/actions/<notifier event>/error

Possible CPU notifier events to be failed are:

 * CPU_UP_PREPARE
 * CPU_UP_PREPARE_FROZEN
 * CPU_DOWN_PREPARE
 * CPU_DOWN_PREPARE_FROZEN

Example1: Inject CPU offline error (-1 == -EPERM)

	# cd /sys/kernel/debug/notifier-error-inject/cpu
	# echo -1 > actions/CPU_DOWN_PREPARE/error
	# echo 0 > /sys/devices/system/cpu/cpu1/online
	bash: echo: write error: Operation not permitted

Example2: inject CPU online error (-2 == -ENOENT)

	# echo -2 > actions/CPU_UP_PREPARE/error
	# echo 1 > /sys/devices/system/cpu/cpu1/online
	bash: echo: write error: No such file or directory

PM notifier error injection module
----------------------------------
This feature is controlled through debugfs interface
/sys/kernel/debug/notifier-error-inject/pm/actions/<notifier event>/error

Possible PM notifier events to be failed are:

 * PM_HIBERNATION_PREPARE
 * PM_SUSPEND_PREPARE
 * PM_RESTORE_PREPARE

Example: Inject PM suspend error (-12 = -ENOMEM)

	# cd /sys/kernel/debug/notifier-error-inject/pm/
	# echo -12 > actions/PM_SUSPEND_PREPARE/error
	# echo mem > /sys/power/state
	bash: echo: write error: Cannot allocate memory

Memory hotplug notifier error injection module
----------------------------------------------
This feature is controlled through debugfs interface
/sys/kernel/debug/notifier-error-inject/memory/actions/<notifier event>/error

Possible memory notifier events to be failed are:

 * MEM_GOING_ONLINE
 * MEM_GOING_OFFLINE

Example: Inject memory hotplug offline error (-12 == -ENOMEM)

	# cd /sys/kernel/debug/notifier-error-inject/memory
	# echo -12 > actions/MEM_GOING_OFFLINE/error
	# echo offline > /sys/devices/system/memory/memoryXXX/state
	bash: echo: write error: Cannot allocate memory

powerpc pSeries reconfig notifier error injection module
--------------------------------------------------------
This feature is controlled through debugfs interface
/sys/kernel/debug/notifier-error-inject/pSeries-reconfig/actions/<notifier event>/error

Possible pSeries reconfig notifier events to be failed are:

 * PSERIES_RECONFIG_ADD
 * PSERIES_RECONFIG_REMOVE
 * PSERIES_DRCONF_MEM_ADD
 * PSERIES_DRCONF_MEM_REMOVE

For more usage examples
-----------------------
There are tools/testing/selftests using the notifier error injection features
for CPU and memory notifiers.

 * tools/testing/selftests/cpu-hotplug/on-off-test.sh
 * tools/testing/selftests/memory-hotplug/on-off-test.sh

These scripts first do simple online and offline tests and then do fault
injection tests if notifier error injection module is available.