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1===========================================
2Fault injection capabilities infrastructure
3===========================================
4
5See also drivers/md/md-faulty.c and "every_nth" module option for scsi_debug.
6
7
8Available fault injection capabilities
9--------------------------------------
10
11- failslab
12
13 injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
14
15- fail_page_alloc
16
17 injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
18
19- fail_futex
20
21 injects futex deadlock and uaddr fault errors.
22
23- fail_make_request
24
25 injects disk IO errors on devices permitted by setting
26 /sys/block/<device>/make-it-fail or
27 /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
28
29- fail_mmc_request
30
31 injects MMC data errors on devices permitted by setting
32 debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
33
34- fail_function
35
36 injects error return on specific functions, which are marked by
37 ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
38 under /sys/kernel/debug/fail_function. No boot option supported.
39
40- NVMe fault injection
41
42 inject NVMe status code and retry flag on devices permitted by setting
43 debugfs entries under /sys/kernel/debug/nvme*/fault_inject. The default
44 status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
45 retry flag can be set via the debugfs.
46
47
48Configure fault-injection capabilities behavior
49-----------------------------------------------
50
51debugfs entries
52^^^^^^^^^^^^^^^
53
54fault-inject-debugfs kernel module provides some debugfs entries for runtime
55configuration of fault-injection capabilities.
56
57- /sys/kernel/debug/fail*/probability:
58
59 likelihood of failure injection, in percent.
60
61 Format: <percent>
62
63 Note that one-failure-per-hundred is a very high error rate
64 for some testcases. Consider setting probability=100 and configure
65 /sys/kernel/debug/fail*/interval for such testcases.
66
67- /sys/kernel/debug/fail*/interval:
68
69 specifies the interval between failures, for calls to
70 should_fail() that pass all the other tests.
71
72 Note that if you enable this, by setting interval>1, you will
73 probably want to set probability=100.
74
75- /sys/kernel/debug/fail*/times:
76
77 specifies how many times failures may happen at most.
78 A value of -1 means "no limit".
79
80- /sys/kernel/debug/fail*/space:
81
82 specifies an initial resource "budget", decremented by "size"
83 on each call to should_fail(,size). Failure injection is
84 suppressed until "space" reaches zero.
85
86- /sys/kernel/debug/fail*/verbose
87
88 Format: { 0 | 1 | 2 }
89
90 specifies the verbosity of the messages when failure is
91 injected. '0' means no messages; '1' will print only a single
92 log line per failure; '2' will print a call trace too -- useful
93 to debug the problems revealed by fault injection.
94
95- /sys/kernel/debug/fail*/task-filter:
96
97 Format: { 'Y' | 'N' }
98
99 A value of 'N' disables filtering by process (default).
100 Any positive value limits failures to only processes indicated by
101 /proc/<pid>/make-it-fail==1.
102
103- /sys/kernel/debug/fail*/require-start,
104 /sys/kernel/debug/fail*/require-end,
105 /sys/kernel/debug/fail*/reject-start,
106 /sys/kernel/debug/fail*/reject-end:
107
108 specifies the range of virtual addresses tested during
109 stacktrace walking. Failure is injected only if some caller
110 in the walked stacktrace lies within the required range, and
111 none lies within the rejected range.
112 Default required range is [0,ULONG_MAX) (whole of virtual address space).
113 Default rejected range is [0,0).
114
115- /sys/kernel/debug/fail*/stacktrace-depth:
116
117 specifies the maximum stacktrace depth walked during search
118 for a caller within [require-start,require-end) OR
119 [reject-start,reject-end).
120
121- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
122
123 Format: { 'Y' | 'N' }
124
125 default is 'N', setting it to 'Y' won't inject failures into
126 highmem/user allocations.
127
128- /sys/kernel/debug/failslab/ignore-gfp-wait:
129- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
130
131 Format: { 'Y' | 'N' }
132
133 default is 'N', setting it to 'Y' will inject failures
134 only into non-sleep allocations (GFP_ATOMIC allocations).
135
136- /sys/kernel/debug/fail_page_alloc/min-order:
137
138 specifies the minimum page allocation order to be injected
139 failures.
140
141- /sys/kernel/debug/fail_futex/ignore-private:
142
143 Format: { 'Y' | 'N' }
144
145 default is 'N', setting it to 'Y' will disable failure injections
146 when dealing with private (address space) futexes.
147
148- /sys/kernel/debug/fail_function/inject:
149
150 Format: { 'function-name' | '!function-name' | '' }
151
152 specifies the target function of error injection by name.
153 If the function name leads '!' prefix, given function is
154 removed from injection list. If nothing specified ('')
155 injection list is cleared.
156
157- /sys/kernel/debug/fail_function/injectable:
158
159 (read only) shows error injectable functions and what type of
160 error values can be specified. The error type will be one of
161 below;
162 - NULL: retval must be 0.
163 - ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
164 - ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).
165
166- /sys/kernel/debug/fail_function/<functiuon-name>/retval:
167
168 specifies the "error" return value to inject to the given
169 function for given function. This will be created when
170 user specifies new injection entry.
171
172Boot option
173^^^^^^^^^^^
174
175In order to inject faults while debugfs is not available (early boot time),
176use the boot option::
177
178 failslab=
179 fail_page_alloc=
180 fail_make_request=
181 fail_futex=
182 mmc_core.fail_request=<interval>,<probability>,<space>,<times>
183
184proc entries
185^^^^^^^^^^^^
186
187- /proc/<pid>/fail-nth,
188 /proc/self/task/<tid>/fail-nth:
189
190 Write to this file of integer N makes N-th call in the task fail.
191 Read from this file returns a integer value. A value of '0' indicates
192 that the fault setup with a previous write to this file was injected.
193 A positive integer N indicates that the fault wasn't yet injected.
194 Note that this file enables all types of faults (slab, futex, etc).
195 This setting takes precedence over all other generic debugfs settings
196 like probability, interval, times, etc. But per-capability settings
197 (e.g. fail_futex/ignore-private) take precedence over it.
198
199 This feature is intended for systematic testing of faults in a single
200 system call. See an example below.
201
202How to add new fault injection capability
203-----------------------------------------
204
205- #include <linux/fault-inject.h>
206
207- define the fault attributes
208
209 DECLARE_FAULT_ATTR(name);
210
211 Please see the definition of struct fault_attr in fault-inject.h
212 for details.
213
214- provide a way to configure fault attributes
215
216- boot option
217
218 If you need to enable the fault injection capability from boot time, you can
219 provide boot option to configure it. There is a helper function for it:
220
221 setup_fault_attr(attr, str);
222
223- debugfs entries
224
225 failslab, fail_page_alloc, and fail_make_request use this way.
226 Helper functions:
227
228 fault_create_debugfs_attr(name, parent, attr);
229
230- module parameters
231
232 If the scope of the fault injection capability is limited to a
233 single kernel module, it is better to provide module parameters to
234 configure the fault attributes.
235
236- add a hook to insert failures
237
238 Upon should_fail() returning true, client code should inject a failure:
239
240 should_fail(attr, size);
241
242Application Examples
243--------------------
244
245- Inject slab allocation failures into module init/exit code::
246
247 #!/bin/bash
248
249 FAILTYPE=failslab
250 echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
251 echo 10 > /sys/kernel/debug/$FAILTYPE/probability
252 echo 100 > /sys/kernel/debug/$FAILTYPE/interval
253 echo -1 > /sys/kernel/debug/$FAILTYPE/times
254 echo 0 > /sys/kernel/debug/$FAILTYPE/space
255 echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
256 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
257
258 faulty_system()
259 {
260 bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
261 }
262
263 if [ $# -eq 0 ]
264 then
265 echo "Usage: $0 modulename [ modulename ... ]"
266 exit 1
267 fi
268
269 for m in $*
270 do
271 echo inserting $m...
272 faulty_system modprobe $m
273
274 echo removing $m...
275 faulty_system modprobe -r $m
276 done
277
278------------------------------------------------------------------------------
279
280- Inject page allocation failures only for a specific module::
281
282 #!/bin/bash
283
284 FAILTYPE=fail_page_alloc
285 module=$1
286
287 if [ -z $module ]
288 then
289 echo "Usage: $0 <modulename>"
290 exit 1
291 fi
292
293 modprobe $module
294
295 if [ ! -d /sys/module/$module/sections ]
296 then
297 echo Module $module is not loaded
298 exit 1
299 fi
300
301 cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
302 cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
303
304 echo N > /sys/kernel/debug/$FAILTYPE/task-filter
305 echo 10 > /sys/kernel/debug/$FAILTYPE/probability
306 echo 100 > /sys/kernel/debug/$FAILTYPE/interval
307 echo -1 > /sys/kernel/debug/$FAILTYPE/times
308 echo 0 > /sys/kernel/debug/$FAILTYPE/space
309 echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
310 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
311 echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
312 echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
313
314 trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
315
316 echo "Injecting errors into the module $module... (interrupt to stop)"
317 sleep 1000000
318
319------------------------------------------------------------------------------
320
321- Inject open_ctree error while btrfs mount::
322
323 #!/bin/bash
324
325 rm -f testfile.img
326 dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
327 DEVICE=$(losetup --show -f testfile.img)
328 mkfs.btrfs -f $DEVICE
329 mkdir -p tmpmnt
330
331 FAILTYPE=fail_function
332 FAILFUNC=open_ctree
333 echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
334 echo -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
335 echo N > /sys/kernel/debug/$FAILTYPE/task-filter
336 echo 100 > /sys/kernel/debug/$FAILTYPE/probability
337 echo 0 > /sys/kernel/debug/$FAILTYPE/interval
338 echo -1 > /sys/kernel/debug/$FAILTYPE/times
339 echo 0 > /sys/kernel/debug/$FAILTYPE/space
340 echo 1 > /sys/kernel/debug/$FAILTYPE/verbose
341
342 mount -t btrfs $DEVICE tmpmnt
343 if [ $? -ne 0 ]
344 then
345 echo "SUCCESS!"
346 else
347 echo "FAILED!"
348 umount tmpmnt
349 fi
350
351 echo > /sys/kernel/debug/$FAILTYPE/inject
352
353 rmdir tmpmnt
354 losetup -d $DEVICE
355 rm testfile.img
356
357
358Tool to run command with failslab or fail_page_alloc
359----------------------------------------------------
360In order to make it easier to accomplish the tasks mentioned above, we can use
361tools/testing/fault-injection/failcmd.sh. Please run a command
362"./tools/testing/fault-injection/failcmd.sh --help" for more information and
363see the following examples.
364
365Examples:
366
367Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
368allocation failure::
369
370 # ./tools/testing/fault-injection/failcmd.sh \
371 -- make -C tools/testing/selftests/ run_tests
372
373Same as above except to specify 100 times failures at most instead of one time
374at most by default::
375
376 # ./tools/testing/fault-injection/failcmd.sh --times=100 \
377 -- make -C tools/testing/selftests/ run_tests
378
379Same as above except to inject page allocation failure instead of slab
380allocation failure::
381
382 # env FAILCMD_TYPE=fail_page_alloc \
383 ./tools/testing/fault-injection/failcmd.sh --times=100 \
384 -- make -C tools/testing/selftests/ run_tests
385
386Systematic faults using fail-nth
387---------------------------------
388
389The following code systematically faults 0-th, 1-st, 2-nd and so on
390capabilities in the socketpair() system call::
391
392 #include <sys/types.h>
393 #include <sys/stat.h>
394 #include <sys/socket.h>
395 #include <sys/syscall.h>
396 #include <fcntl.h>
397 #include <unistd.h>
398 #include <string.h>
399 #include <stdlib.h>
400 #include <stdio.h>
401 #include <errno.h>
402
403 int main()
404 {
405 int i, err, res, fail_nth, fds[2];
406 char buf[128];
407
408 system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
409 sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
410 fail_nth = open(buf, O_RDWR);
411 for (i = 1;; i++) {
412 sprintf(buf, "%d", i);
413 write(fail_nth, buf, strlen(buf));
414 res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
415 err = errno;
416 pread(fail_nth, buf, sizeof(buf), 0);
417 if (res == 0) {
418 close(fds[0]);
419 close(fds[1]);
420 }
421 printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
422 res, err);
423 if (atoi(buf))
424 break;
425 }
426 return 0;
427 }
428
429An example output::
430
431 1-th fault Y: res=-1/23
432 2-th fault Y: res=-1/23
433 3-th fault Y: res=-1/12
434 4-th fault Y: res=-1/12
435 5-th fault Y: res=-1/23
436 6-th fault Y: res=-1/23
437 7-th fault Y: res=-1/23
438 8-th fault Y: res=-1/12
439 9-th fault Y: res=-1/12
440 10-th fault Y: res=-1/12
441 11-th fault Y: res=-1/12
442 12-th fault Y: res=-1/12
443 13-th fault Y: res=-1/12
444 14-th fault Y: res=-1/12
445 15-th fault Y: res=-1/12
446 16-th fault N: res=0/12