Documentation/fault-injection/fault-injection.txt

   1 Fault injection capabilities infrastructure
   2 ===========================================
   3
   4 See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
   5
   6
   7 Available fault injection capabilities
   8 --------------------------------------
   9
  10 o failslab
  11
  12   injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
  13
  14 o fail_page_alloc
  15
  16   injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
  17
  18 o fail_make_request
  19
  20   injects disk IO errors on devices permitted by setting
  21   /sys/block/<device>/make-it-fail or
  22   /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
  23
  24 Configure fault-injection capabilities behavior
  25 -----------------------------------------------
  26
  27 o debugfs entries
  28
  29 fault-inject-debugfs kernel module provides some debugfs entries for runtime
  30 configuration of fault-injection capabilities.
  31
  32 - /sys/kernel/debug/fail*/probability:
  33
  34         likelihood of failure injection, in percent.
  35         Format: <percent>
  36
  37         Note that one-failure-per-hundred is a very high error rate
  38         for some testcases.  Consider setting probability=100 and configure
  39         /sys/kernel/debug/fail*/interval for such testcases.
  40
  41 - /sys/kernel/debug/fail*/interval:
  42
  43         specifies the interval between failures, for calls to
  44         should_fail() that pass all the other tests.
  45
  46         Note that if you enable this, by setting interval>1, you will
  47         probably want to set probability=100.
  48
  49 - /sys/kernel/debug/fail*/times:
  50
  51         specifies how many times failures may happen at most.
  52         A value of -1 means "no limit".
  53
  54 - /sys/kernel/debug/fail*/space:
  55
  56         specifies an initial resource "budget", decremented by "size"
  57         on each call to should_fail(,size).  Failure injection is
  58         suppressed until "space" reaches zero.
  59
  60 - /sys/kernel/debug/fail*/verbose
  61
  62         Format: { 0 | 1 | 2 }
  63         specifies the verbosity of the messages when failure is
  64         injected.  '0' means no messages; '1' will print only a single
  65         log line per failure; '2' will print a call trace too -- useful
  66         to debug the problems revealed by fault injection.
  67
  68 - /sys/kernel/debug/fail*/task-filter:
  69
  70         Format: { 'Y' | 'N' }
  71         A value of 'N' disables filtering by process (default).
  72         Any positive value limits failures to only processes indicated by
  73         /proc/<pid>/make-it-fail==1.
  74
  75 - /sys/kernel/debug/fail*/require-start:
  76 - /sys/kernel/debug/fail*/require-end:
  77 - /sys/kernel/debug/fail*/reject-start:
  78 - /sys/kernel/debug/fail*/reject-end:
  79
  80         specifies the range of virtual addresses tested during
  81         stacktrace walking.  Failure is injected only if some caller
  82         in the walked stacktrace lies within the required range, and
  83         none lies within the rejected range.
  84         Default required range is [0,ULONG_MAX) (whole of virtual address space).
  85         Default rejected range is [0,0).
  86
  87 - /sys/kernel/debug/fail*/stacktrace-depth:
  88
  89         specifies the maximum stacktrace depth walked during search
  90         for a caller within [require-start,require-end) OR
  91         [reject-start,reject-end).
  92
  93 - /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
  94
  95         Format: { 'Y' | 'N' }
  96         default is 'N', setting it to 'Y' won't inject failures into
  97         highmem/user allocations.
  98
  99 - /sys/kernel/debug/failslab/ignore-gfp-wait:
 100 - /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
 101
 102         Format: { 'Y' | 'N' }
 103         default is 'N', setting it to 'Y' will inject failures
 104         only into non-sleep allocations (GFP_ATOMIC allocations).
 105
 106 - /sys/kernel/debug/fail_page_alloc/min-order:
 107
 108         specifies the minimum page allocation order to be injected
 109         failures.
 110
 111 o Boot option
 112
 113 In order to inject faults while debugfs is not available (early boot time),
 114 use the boot option:
 115
 116         failslab=
 117         fail_page_alloc=
 118         fail_make_request=<interval>,<probability>,<space>,<times>
 119
 120 How to add new fault injection capability
 121 -----------------------------------------
 122
 123 o #include <linux/fault-inject.h>
 124
 125 o define the fault attributes
 126
 127   DECLARE_FAULT_INJECTION(name);
 128
 129   Please see the definition of struct fault_attr in fault-inject.h
 130   for details.
 131
 132 o provide a way to configure fault attributes
 133
 134 - boot option
 135
 136   If you need to enable the fault injection capability from boot time, you can
 137   provide boot option to configure it. There is a helper function for it:
 138
 139         setup_fault_attr(attr, str);
 140
 141 - debugfs entries
 142
 143   failslab, fail_page_alloc, and fail_make_request use this way.
 144   Helper functions:
 145
 146         fault_create_debugfs_attr(name, parent, attr);
 147
 148 - module parameters
 149
 150   If the scope of the fault injection capability is limited to a
 151   single kernel module, it is better to provide module parameters to
 152   configure the fault attributes.
 153
 154 o add a hook to insert failures
 155
 156   Upon should_fail() returning true, client code should inject a failure.
 157
 158         should_fail(attr, size);
 159
 160 Application Examples
 161 --------------------
 162
 163 o Inject slab allocation failures into module init/exit code
 164
 165 #!/bin/bash
 166
 167 FAILTYPE=failslab
 168 echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
 169 echo 10 > /sys/kernel/debug/$FAILTYPE/probability
 170 echo 100 > /sys/kernel/debug/$FAILTYPE/interval
 171 echo -1 > /sys/kernel/debug/$FAILTYPE/times
 172 echo 0 > /sys/kernel/debug/$FAILTYPE/space
 173 echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
 174 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
 175
 176 faulty_system()
 177 {
 178         bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
 179 }
 180
 181 if [ $# -eq 0 ]
 182 then
 183         echo "Usage: $0 modulename [ modulename ... ]"
 184         exit 1
 185 fi
 186
 187 for m in $*
 188 do
 189         echo inserting $m...
 190         faulty_system modprobe $m
 191
 192         echo removing $m...
 193         faulty_system modprobe -r $m
 194 done
 195
 196 ------------------------------------------------------------------------------
 197
 198 o Inject page allocation failures only for a specific module
 199
 200 #!/bin/bash
 201
 202 FAILTYPE=fail_page_alloc
 203 module=$1
 204
 205 if [ -z $module ]
 206 then
 207         echo "Usage: $0 <modulename>"
 208         exit 1
 209 fi
 210
 211 modprobe $module
 212
 213 if [ ! -d /sys/module/$module/sections ]
 214 then
 215         echo Module $module is not loaded
 216         exit 1
 217 fi
 218
 219 cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
 220 cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
 221
 222 echo N > /sys/kernel/debug/$FAILTYPE/task-filter
 223 echo 10 > /sys/kernel/debug/$FAILTYPE/probability
 224 echo 100 > /sys/kernel/debug/$FAILTYPE/interval
 225 echo -1 > /sys/kernel/debug/$FAILTYPE/times
 226 echo 0 > /sys/kernel/debug/$FAILTYPE/space
 227 echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
 228 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
 229 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
 230 echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
 231
 232 trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
 233
 234 echo "Injecting errors into the module $module... (interrupt to stop)"
 235 sleep 1000000
 236