222 lines
5.5 KiB
Plaintext
222 lines
5.5 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_make_request
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injects disk IO errors on permitted devices by
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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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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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- /debug/*/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-handred is a very high error rate
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for some testcases. Please set probably=100 and configure
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/debug/*/interval for such testcases.
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- /debug/*/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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- /debug/*/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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- /debug/*/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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- /debug/*/verbose
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Format: { 0 | 1 | 2 }
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specifies the verbosity of the messages when failure is injected.
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We default to 0 (no extra messages), setting it to '1' will
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print only to tell failure happened, '2' will print call trace too -
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it is useful to debug the problems revealed by fault injection
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capabilities.
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- /debug/*/task-filter:
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Format: { 0 | 1 }
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A value of '0' 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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- /debug/*/address-start:
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- /debug/*/address-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 this range.
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Default is [0,ULONG_MAX) (whole of virtual address space).
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- /debug/*/stacktrace-depth:
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specifies the maximum stacktrace depth walked during search
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for a caller within [address-start,address-end).
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- /debug/fail_page_alloc/ignore-gfp-highmem:
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Format: { 0 | 1 }
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default is 0, setting it to '1' won't inject failures into
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highmem/user allocations.
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- /debug/failslab/ignore-gfp-wait:
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- /debug/fail_page_alloc/ignore-gfp-wait:
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Format: { 0 | 1 }
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default is 0, setting it to '1' will inject failures
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only into non-sleep allocations (GFP_ATOMIC allocations).
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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=<interval>,<probability>,<space>,<times>
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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 the 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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There is a helper function for it.
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init_fault_attr_entries(entries, attr, name);
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void cleanup_fault_attr_entries(entries);
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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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should_fail() returns 1 when failures should happen.
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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/cleanup code
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------------------------------------------------------------------------------
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#!/bin/bash
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FAILCMD=Documentation/fault-injection/failcmd.sh
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BLACKLIST="root_plug evbug"
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FAILNAME=failslab
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echo Y > /debug/$FAILNAME/task-filter
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echo 10 > /debug/$FAILNAME/probability
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echo 100 > /debug/$FAILNAME/interval
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echo -1 > /debug/$FAILNAME/times
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echo 2 > /debug/$FAILNAME/verbose
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echo 1 > /debug/$FAILNAME/ignore-gfp-wait
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blacklist()
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{
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echo $BLACKLIST | grep $1 > /dev/null 2>&1
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}
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oops()
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{
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dmesg | grep BUG > /dev/null 2>&1
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}
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find /lib/modules/`uname -r` -name '*.ko' -exec basename {} .ko \; |
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while read i
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do
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oops && exit 1
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if ! blacklist $i
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then
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echo inserting $i...
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bash $FAILCMD modprobe $i
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fi
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done
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lsmod | awk '{ if ($3 == 0) { print $1 } }' |
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while read i
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do
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oops && exit 1
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if ! blacklist $i
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then
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echo removing $i...
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bash $FAILCMD modprobe -r $i
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fi
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done
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------------------------------------------------------------------------------
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o inject slab allocation failures only for a specific module
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------------------------------------------------------------------------------
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#!/bin/bash
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FAILMOD=Documentation/fault-injection/failmodule.sh
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echo injecting errors into the module $1...
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modprobe $1
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bash $FAILMOD failslab $1 10
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echo 25 > /debug/failslab/probability
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------------------------------------------------------------------------------
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