360 lines
9.9 KiB
Plaintext
360 lines
9.9 KiB
Plaintext
Fault injection capabilities infrastructure
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===========================================
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See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
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Available fault injection capabilities
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--------------------------------------
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o failslab
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injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
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o fail_page_alloc
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injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
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o fail_futex
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injects futex deadlock and uaddr fault errors.
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o fail_make_request
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injects disk IO errors on devices permitted by setting
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/sys/block/<device>/make-it-fail or
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/sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
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o fail_mmc_request
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injects MMC data errors on devices permitted by setting
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debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
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Configure fault-injection capabilities behavior
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-----------------------------------------------
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o debugfs entries
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fault-inject-debugfs kernel module provides some debugfs entries for runtime
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configuration of fault-injection capabilities.
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- /sys/kernel/debug/fail*/probability:
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likelihood of failure injection, in percent.
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Format: <percent>
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Note that one-failure-per-hundred is a very high error rate
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for some testcases. Consider setting probability=100 and configure
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/sys/kernel/debug/fail*/interval for such testcases.
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- /sys/kernel/debug/fail*/interval:
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specifies the interval between failures, for calls to
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should_fail() that pass all the other tests.
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Note that if you enable this, by setting interval>1, you will
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probably want to set probability=100.
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- /sys/kernel/debug/fail*/times:
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specifies how many times failures may happen at most.
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A value of -1 means "no limit".
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- /sys/kernel/debug/fail*/space:
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specifies an initial resource "budget", decremented by "size"
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on each call to should_fail(,size). Failure injection is
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suppressed until "space" reaches zero.
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- /sys/kernel/debug/fail*/verbose
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Format: { 0 | 1 | 2 }
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specifies the verbosity of the messages when failure is
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injected. '0' means no messages; '1' will print only a single
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log line per failure; '2' will print a call trace too -- useful
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to debug the problems revealed by fault injection.
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- /sys/kernel/debug/fail*/task-filter:
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Format: { 'Y' | 'N' }
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A value of 'N' disables filtering by process (default).
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Any positive value limits failures to only processes indicated by
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/proc/<pid>/make-it-fail==1.
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- /sys/kernel/debug/fail*/require-start:
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- /sys/kernel/debug/fail*/require-end:
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- /sys/kernel/debug/fail*/reject-start:
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- /sys/kernel/debug/fail*/reject-end:
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specifies the range of virtual addresses tested during
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stacktrace walking. Failure is injected only if some caller
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in the walked stacktrace lies within the required range, and
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none lies within the rejected range.
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Default required range is [0,ULONG_MAX) (whole of virtual address space).
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Default rejected range is [0,0).
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- /sys/kernel/debug/fail*/stacktrace-depth:
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specifies the maximum stacktrace depth walked during search
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for a caller within [require-start,require-end) OR
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[reject-start,reject-end).
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- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' won't inject failures into
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highmem/user allocations.
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- /sys/kernel/debug/failslab/ignore-gfp-wait:
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- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' will inject failures
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only into non-sleep allocations (GFP_ATOMIC allocations).
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- /sys/kernel/debug/fail_page_alloc/min-order:
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specifies the minimum page allocation order to be injected
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failures.
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- /sys/kernel/debug/fail_futex/ignore-private:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' will disable failure injections
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when dealing with private (address space) futexes.
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o Boot option
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In order to inject faults while debugfs is not available (early boot time),
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use the boot option:
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failslab=
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fail_page_alloc=
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fail_make_request=
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fail_futex=
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mmc_core.fail_request=<interval>,<probability>,<space>,<times>
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o proc entries
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- /proc/<pid>/fail-nth:
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- /proc/self/task/<tid>/fail-nth:
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Write to this file of integer N makes N-th call in the task fail.
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Read from this file returns a integer value. A value of '0' indicates
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that the fault setup with a previous write to this file was injected.
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A positive integer N indicates that the fault wasn't yet injected.
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Note that this file enables all types of faults (slab, futex, etc).
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This setting takes precedence over all other generic debugfs settings
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like probability, interval, times, etc. But per-capability settings
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(e.g. fail_futex/ignore-private) take precedence over it.
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This feature is intended for systematic testing of faults in a single
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system call. See an example below.
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How to add new fault injection capability
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-----------------------------------------
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o #include <linux/fault-inject.h>
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o define the fault attributes
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DECLARE_FAULT_INJECTION(name);
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Please see the definition of struct fault_attr in fault-inject.h
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for details.
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o provide a way to configure fault attributes
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- boot option
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If you need to enable the fault injection capability from boot time, you can
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provide boot option to configure it. There is a helper function for it:
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setup_fault_attr(attr, str);
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- debugfs entries
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failslab, fail_page_alloc, and fail_make_request use this way.
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Helper functions:
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fault_create_debugfs_attr(name, parent, attr);
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- module parameters
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If the scope of the fault injection capability is limited to a
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single kernel module, it is better to provide module parameters to
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configure the fault attributes.
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o add a hook to insert failures
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Upon should_fail() returning true, client code should inject a failure.
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should_fail(attr, size);
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Application Examples
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--------------------
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o Inject slab allocation failures into module init/exit code
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#!/bin/bash
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FAILTYPE=failslab
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echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
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echo 10 > /sys/kernel/debug/$FAILTYPE/probability
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echo 100 > /sys/kernel/debug/$FAILTYPE/interval
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echo -1 > /sys/kernel/debug/$FAILTYPE/times
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echo 0 > /sys/kernel/debug/$FAILTYPE/space
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echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
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faulty_system()
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{
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bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
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}
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if [ $# -eq 0 ]
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then
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echo "Usage: $0 modulename [ modulename ... ]"
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exit 1
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fi
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for m in $*
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do
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echo inserting $m...
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faulty_system modprobe $m
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echo removing $m...
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faulty_system modprobe -r $m
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done
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------------------------------------------------------------------------------
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o Inject page allocation failures only for a specific module
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#!/bin/bash
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FAILTYPE=fail_page_alloc
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module=$1
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if [ -z $module ]
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then
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echo "Usage: $0 <modulename>"
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exit 1
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fi
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modprobe $module
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if [ ! -d /sys/module/$module/sections ]
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then
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echo Module $module is not loaded
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exit 1
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fi
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cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
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cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
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echo N > /sys/kernel/debug/$FAILTYPE/task-filter
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echo 10 > /sys/kernel/debug/$FAILTYPE/probability
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echo 100 > /sys/kernel/debug/$FAILTYPE/interval
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echo -1 > /sys/kernel/debug/$FAILTYPE/times
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echo 0 > /sys/kernel/debug/$FAILTYPE/space
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echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
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echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
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trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
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echo "Injecting errors into the module $module... (interrupt to stop)"
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sleep 1000000
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Tool to run command with failslab or fail_page_alloc
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----------------------------------------------------
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In order to make it easier to accomplish the tasks mentioned above, we can use
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tools/testing/fault-injection/failcmd.sh. Please run a command
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"./tools/testing/fault-injection/failcmd.sh --help" for more information and
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see the following examples.
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Examples:
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Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
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allocation failure.
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# ./tools/testing/fault-injection/failcmd.sh \
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-- make -C tools/testing/selftests/ run_tests
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Same as above except to specify 100 times failures at most instead of one time
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at most by default.
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# ./tools/testing/fault-injection/failcmd.sh --times=100 \
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-- make -C tools/testing/selftests/ run_tests
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Same as above except to inject page allocation failure instead of slab
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allocation failure.
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# env FAILCMD_TYPE=fail_page_alloc \
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./tools/testing/fault-injection/failcmd.sh --times=100 \
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-- make -C tools/testing/selftests/ run_tests
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Systematic faults using fail-nth
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---------------------------------
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The following code systematically faults 0-th, 1-st, 2-nd and so on
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capabilities in the socketpair() system call.
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/socket.h>
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#include <sys/syscall.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <string.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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int main()
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{
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int i, err, res, fail_nth, fds[2];
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char buf[128];
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system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
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sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
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fail_nth = open(buf, O_RDWR);
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for (i = 1;; i++) {
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sprintf(buf, "%d", i);
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write(fail_nth, buf, strlen(buf));
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res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
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err = errno;
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pread(fail_nth, buf, sizeof(buf), 0);
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if (res == 0) {
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close(fds[0]);
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close(fds[1]);
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}
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printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
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res, err);
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if (atoi(buf))
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break;
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}
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return 0;
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}
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An example output:
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1-th fault Y: res=-1/23
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2-th fault Y: res=-1/23
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3-th fault Y: res=-1/12
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4-th fault Y: res=-1/12
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5-th fault Y: res=-1/23
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6-th fault Y: res=-1/23
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7-th fault Y: res=-1/23
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8-th fault Y: res=-1/12
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9-th fault Y: res=-1/12
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10-th fault Y: res=-1/12
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11-th fault Y: res=-1/12
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12-th fault Y: res=-1/12
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13-th fault Y: res=-1/12
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14-th fault Y: res=-1/12
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15-th fault Y: res=-1/12
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16-th fault N: res=0/12
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