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Based on kernel version 3.9. Page generated on 2013-05-02 23:05 EST.

	Fault injection capabilities infrastructure
	===========================================
	
	See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
	
	
	Available fault injection capabilities
	--------------------------------------
	
	o failslab
	
	  injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
	
	o fail_page_alloc
	
	  injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
	
	o fail_make_request
	
	  injects disk IO errors on devices permitted by setting
	  /sys/block/<device>/make-it-fail or
	  /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
	
	o fail_mmc_request
	
	  injects MMC data errors on devices permitted by setting
	  debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
	
	Configure fault-injection capabilities behavior
	-----------------------------------------------
	
	o debugfs entries
	
	fault-inject-debugfs kernel module provides some debugfs entries for runtime
	configuration of fault-injection capabilities.
	
	- /sys/kernel/debug/fail*/probability:
	
		likelihood of failure injection, in percent.
		Format: <percent>
	
		Note that one-failure-per-hundred is a very high error rate
		for some testcases.  Consider setting probability=100 and configure
		/sys/kernel/debug/fail*/interval for such testcases.
	
	- /sys/kernel/debug/fail*/interval:
	
		specifies the interval between failures, for calls to
		should_fail() that pass all the other tests.
	
		Note that if you enable this, by setting interval>1, you will
		probably want to set probability=100.
	
	- /sys/kernel/debug/fail*/times:
	
		specifies how many times failures may happen at most.
		A value of -1 means "no limit".
	
	- /sys/kernel/debug/fail*/space:
	
		specifies an initial resource "budget", decremented by "size"
		on each call to should_fail(,size).  Failure injection is
		suppressed until "space" reaches zero.
	
	- /sys/kernel/debug/fail*/verbose
	
		Format: { 0 | 1 | 2 }
		specifies the verbosity of the messages when failure is
		injected.  '0' means no messages; '1' will print only a single
		log line per failure; '2' will print a call trace too -- useful
		to debug the problems revealed by fault injection.
	
	- /sys/kernel/debug/fail*/task-filter:
	
		Format: { 'Y' | 'N' }
		A value of 'N' disables filtering by process (default).
		Any positive value limits failures to only processes indicated by
		/proc/<pid>/make-it-fail==1.
	
	- /sys/kernel/debug/fail*/require-start:
	- /sys/kernel/debug/fail*/require-end:
	- /sys/kernel/debug/fail*/reject-start:
	- /sys/kernel/debug/fail*/reject-end:
	
		specifies the range of virtual addresses tested during
		stacktrace walking.  Failure is injected only if some caller
		in the walked stacktrace lies within the required range, and
		none lies within the rejected range.
		Default required range is [0,ULONG_MAX) (whole of virtual address space).
		Default rejected range is [0,0).
	
	- /sys/kernel/debug/fail*/stacktrace-depth:
	
		specifies the maximum stacktrace depth walked during search
		for a caller within [require-start,require-end) OR
		[reject-start,reject-end).
	
	- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
	
		Format: { 'Y' | 'N' }
		default is 'N', setting it to 'Y' won't inject failures into
		highmem/user allocations.
	
	- /sys/kernel/debug/failslab/ignore-gfp-wait:
	- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
	
		Format: { 'Y' | 'N' }
		default is 'N', setting it to 'Y' will inject failures
		only into non-sleep allocations (GFP_ATOMIC allocations).
	
	- /sys/kernel/debug/fail_page_alloc/min-order:
	
		specifies the minimum page allocation order to be injected
		failures.
	
	o Boot option
	
	In order to inject faults while debugfs is not available (early boot time),
	use the boot option:
	
		failslab=
		fail_page_alloc=
		fail_make_request=
		mmc_core.fail_request=<interval>,<probability>,<space>,<times>
	
	How to add new fault injection capability
	-----------------------------------------
	
	o #include <linux/fault-inject.h>
	
	o define the fault attributes
	
	  DECLARE_FAULT_INJECTION(name);
	
	  Please see the definition of struct fault_attr in fault-inject.h
	  for details.
	
	o provide a way to configure fault attributes
	
	- boot option
	
	  If you need to enable the fault injection capability from boot time, you can
	  provide boot option to configure it. There is a helper function for it:
	
		setup_fault_attr(attr, str);
	
	- debugfs entries
	
	  failslab, fail_page_alloc, and fail_make_request use this way.
	  Helper functions:
	
		fault_create_debugfs_attr(name, parent, attr);
	
	- module parameters
	
	  If the scope of the fault injection capability is limited to a
	  single kernel module, it is better to provide module parameters to
	  configure the fault attributes.
	
	o add a hook to insert failures
	
	  Upon should_fail() returning true, client code should inject a failure.
	
		should_fail(attr, size);
	
	Application Examples
	--------------------
	
	o Inject slab allocation failures into module init/exit code
	
	#!/bin/bash
	
	FAILTYPE=failslab
	echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
	echo 10 > /sys/kernel/debug/$FAILTYPE/probability
	echo 100 > /sys/kernel/debug/$FAILTYPE/interval
	echo -1 > /sys/kernel/debug/$FAILTYPE/times
	echo 0 > /sys/kernel/debug/$FAILTYPE/space
	echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
	echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
	
	faulty_system()
	{
		bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
	}
	
	if [ $# -eq 0 ]
	then
		echo "Usage: $0 modulename [ modulename ... ]"
		exit 1
	fi
	
	for m in $*
	do
		echo inserting $m...
		faulty_system modprobe $m
	
		echo removing $m...
		faulty_system modprobe -r $m
	done
	
	------------------------------------------------------------------------------
	
	o Inject page allocation failures only for a specific module
	
	#!/bin/bash
	
	FAILTYPE=fail_page_alloc
	module=$1
	
	if [ -z $module ]
	then
		echo "Usage: $0 <modulename>"
		exit 1
	fi
	
	modprobe $module
	
	if [ ! -d /sys/module/$module/sections ]
	then
		echo Module $module is not loaded
		exit 1
	fi
	
	cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
	cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
	
	echo N > /sys/kernel/debug/$FAILTYPE/task-filter
	echo 10 > /sys/kernel/debug/$FAILTYPE/probability
	echo 100 > /sys/kernel/debug/$FAILTYPE/interval
	echo -1 > /sys/kernel/debug/$FAILTYPE/times
	echo 0 > /sys/kernel/debug/$FAILTYPE/space
	echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
	echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
	echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
	echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
	
	trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
	
	echo "Injecting errors into the module $module... (interrupt to stop)"
	sleep 1000000
	
	Tool to run command with failslab or fail_page_alloc
	----------------------------------------------------
	In order to make it easier to accomplish the tasks mentioned above, we can use
	tools/testing/fault-injection/failcmd.sh.  Please run a command
	"./tools/testing/fault-injection/failcmd.sh --help" for more information and
	see the following examples.
	
	Examples:
	
	Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
	allocation failure.
	
		# ./tools/testing/fault-injection/failcmd.sh \
			-- make -C tools/testing/selftests/ run_tests
	
	Same as above except to specify 100 times failures at most instead of one time
	at most by default.
	
		# ./tools/testing/fault-injection/failcmd.sh --times=100 \
			-- make -C tools/testing/selftests/ run_tests
	
	Same as above except to inject page allocation failure instead of slab
	allocation failure.
	
		# env FAILCMD_TYPE=fail_page_alloc \
			./tools/testing/fault-injection/failcmd.sh --times=100 \
	                -- make -C tools/testing/selftests/ run_tests

• [ Documentation ]
• fault-injection.txt
• notifier-error-inject.txt
• provoke-crashes.txt
•