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_usercopy
20
21  injects failures in user memory access functions. (copy_from_user(), get_user(), ...)
22
23- fail_futex
24
25  injects futex deadlock and uaddr fault errors.
26
27- fail_sunrpc
28
29  injects kernel RPC client and server failures.
30
31- fail_make_request
32
33  injects disk IO errors on devices permitted by setting
34  /sys/block/<device>/make-it-fail or
35  /sys/block/<device>/<partition>/make-it-fail. (submit_bio_noacct())
36
37- fail_mmc_request
38
39  injects MMC data errors on devices permitted by setting
40  debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
41
42- fail_function
43
44  injects error return on specific functions, which are marked by
45  ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
46  under /sys/kernel/debug/fail_function. No boot option supported.
47
48- NVMe fault injection
49
50  inject NVMe status code and retry flag on devices permitted by setting
51  debugfs entries under /sys/kernel/debug/nvme*/fault_inject. The default
52  status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
53  retry flag can be set via the debugfs.
54
55
56Configure fault-injection capabilities behavior
57-----------------------------------------------
58
59debugfs entries
60^^^^^^^^^^^^^^^
61
62fault-inject-debugfs kernel module provides some debugfs entries for runtime
63configuration of fault-injection capabilities.
64
65- /sys/kernel/debug/fail*/probability:
66
67	likelihood of failure injection, in percent.
68
69	Format: <percent>
70
71	Note that one-failure-per-hundred is a very high error rate
72	for some testcases.  Consider setting probability=100 and configure
73	/sys/kernel/debug/fail*/interval for such testcases.
74
75- /sys/kernel/debug/fail*/interval:
76
77	specifies the interval between failures, for calls to
78	should_fail() that pass all the other tests.
79
80	Note that if you enable this, by setting interval>1, you will
81	probably want to set probability=100.
82
83- /sys/kernel/debug/fail*/times:
84
85	specifies how many times failures may happen at most. A value of -1
86	means "no limit". Note, though, that this file only accepts unsigned
87	values. So, if you want to specify -1, you better use 'printf' instead
88	of 'echo', e.g.: $ printf %#x -1 > times
89
90- /sys/kernel/debug/fail*/space:
91
92	specifies an initial resource "budget", decremented by "size"
93	on each call to should_fail(,size).  Failure injection is
94	suppressed until "space" reaches zero.
95
96- /sys/kernel/debug/fail*/verbose
97
98	Format: { 0 | 1 | 2 }
99
100	specifies the verbosity of the messages when failure is
101	injected.  '0' means no messages; '1' will print only a single
102	log line per failure; '2' will print a call trace too -- useful
103	to debug the problems revealed by fault injection.
104
105- /sys/kernel/debug/fail*/task-filter:
106
107	Format: { 'Y' | 'N' }
108
109	A value of 'N' disables filtering by process (default).
110	Any positive value limits failures to only processes indicated by
111	/proc/<pid>/make-it-fail==1.
112
113- /sys/kernel/debug/fail*/require-start,
114  /sys/kernel/debug/fail*/require-end,
115  /sys/kernel/debug/fail*/reject-start,
116  /sys/kernel/debug/fail*/reject-end:
117
118	specifies the range of virtual addresses tested during
119	stacktrace walking.  Failure is injected only if some caller
120	in the walked stacktrace lies within the required range, and
121	none lies within the rejected range.
122	Default required range is [0,ULONG_MAX) (whole of virtual address space).
123	Default rejected range is [0,0).
124
125- /sys/kernel/debug/fail*/stacktrace-depth:
126
127	specifies the maximum stacktrace depth walked during search
128	for a caller within [require-start,require-end) OR
129	[reject-start,reject-end).
130
131- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
132
133	Format: { 'Y' | 'N' }
134
135	default is 'Y', setting it to 'N' will also inject failures into
136	highmem/user allocations (__GFP_HIGHMEM allocations).
137
138- /sys/kernel/debug/failslab/ignore-gfp-wait:
139- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
140
141	Format: { 'Y' | 'N' }
142
143	default is 'Y', setting it to 'N' will also inject failures
144	into allocations that can sleep (__GFP_DIRECT_RECLAIM allocations).
145
146- /sys/kernel/debug/fail_page_alloc/min-order:
147
148	specifies the minimum page allocation order to be injected
149	failures.
150
151- /sys/kernel/debug/fail_futex/ignore-private:
152
153	Format: { 'Y' | 'N' }
154
155	default is 'N', setting it to 'Y' will disable failure injections
156	when dealing with private (address space) futexes.
157
158- /sys/kernel/debug/fail_sunrpc/ignore-client-disconnect:
159
160	Format: { 'Y' | 'N' }
161
162	default is 'N', setting it to 'Y' will disable disconnect
163	injection on the RPC client.
164
165- /sys/kernel/debug/fail_sunrpc/ignore-server-disconnect:
166
167	Format: { 'Y' | 'N' }
168
169	default is 'N', setting it to 'Y' will disable disconnect
170	injection on the RPC server.
171
172- /sys/kernel/debug/fail_function/inject:
173
174	Format: { 'function-name' | '!function-name' | '' }
175
176	specifies the target function of error injection by name.
177	If the function name leads '!' prefix, given function is
178	removed from injection list. If nothing specified ('')
179	injection list is cleared.
180
181- /sys/kernel/debug/fail_function/injectable:
182
183	(read only) shows error injectable functions and what type of
184	error values can be specified. The error type will be one of
185	below;
186	- NULL:	retval must be 0.
187	- ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
188	- ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).
189
190- /sys/kernel/debug/fail_function/<function-name>/retval:
191
192	specifies the "error" return value to inject to the given function.
193	This will be created when the user specifies a new injection entry.
194	Note that this file only accepts unsigned values. So, if you want to
195	use a negative errno, you better use 'printf' instead of 'echo', e.g.:
196	$ printf %#x -12 > retval
197
198Boot option
199^^^^^^^^^^^
200
201In order to inject faults while debugfs is not available (early boot time),
202use the boot option::
203
204	failslab=
205	fail_page_alloc=
206	fail_usercopy=
207	fail_make_request=
208	fail_futex=
209	mmc_core.fail_request=<interval>,<probability>,<space>,<times>
210
211proc entries
212^^^^^^^^^^^^
213
214- /proc/<pid>/fail-nth,
215  /proc/self/task/<tid>/fail-nth:
216
217	Write to this file of integer N makes N-th call in the task fail.
218	Read from this file returns a integer value. A value of '0' indicates
219	that the fault setup with a previous write to this file was injected.
220	A positive integer N indicates that the fault wasn't yet injected.
221	Note that this file enables all types of faults (slab, futex, etc).
222	This setting takes precedence over all other generic debugfs settings
223	like probability, interval, times, etc. But per-capability settings
224	(e.g. fail_futex/ignore-private) take precedence over it.
225
226	This feature is intended for systematic testing of faults in a single
227	system call. See an example below.
228
229How to add new fault injection capability
230-----------------------------------------
231
232- #include <linux/fault-inject.h>
233
234- define the fault attributes
235
236  DECLARE_FAULT_ATTR(name);
237
238  Please see the definition of struct fault_attr in fault-inject.h
239  for details.
240
241- provide a way to configure fault attributes
242
243- boot option
244
245  If you need to enable the fault injection capability from boot time, you can
246  provide boot option to configure it. There is a helper function for it:
247
248	setup_fault_attr(attr, str);
249
250- debugfs entries
251
252  failslab, fail_page_alloc, fail_usercopy, and fail_make_request use this way.
253  Helper functions:
254
255	fault_create_debugfs_attr(name, parent, attr);
256
257- module parameters
258
259  If the scope of the fault injection capability is limited to a
260  single kernel module, it is better to provide module parameters to
261  configure the fault attributes.
262
263- add a hook to insert failures
264
265  Upon should_fail() returning true, client code should inject a failure:
266
267	should_fail(attr, size);
268
269Application Examples
270--------------------
271
272- Inject slab allocation failures into module init/exit code::
273
274    #!/bin/bash
275
276    FAILTYPE=failslab
277    echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
278    echo 10 > /sys/kernel/debug/$FAILTYPE/probability
279    echo 100 > /sys/kernel/debug/$FAILTYPE/interval
280    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
281    echo 0 > /sys/kernel/debug/$FAILTYPE/space
282    echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
283    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
284
285    faulty_system()
286    {
287	bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
288    }
289
290    if [ $# -eq 0 ]
291    then
292	echo "Usage: $0 modulename [ modulename ... ]"
293	exit 1
294    fi
295
296    for m in $*
297    do
298	echo inserting $m...
299	faulty_system modprobe $m
300
301	echo removing $m...
302	faulty_system modprobe -r $m
303    done
304
305------------------------------------------------------------------------------
306
307- Inject page allocation failures only for a specific module::
308
309    #!/bin/bash
310
311    FAILTYPE=fail_page_alloc
312    module=$1
313
314    if [ -z $module ]
315    then
316	echo "Usage: $0 <modulename>"
317	exit 1
318    fi
319
320    modprobe $module
321
322    if [ ! -d /sys/module/$module/sections ]
323    then
324	echo Module $module is not loaded
325	exit 1
326    fi
327
328    cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
329    cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
330
331    echo N > /sys/kernel/debug/$FAILTYPE/task-filter
332    echo 10 > /sys/kernel/debug/$FAILTYPE/probability
333    echo 100 > /sys/kernel/debug/$FAILTYPE/interval
334    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
335    echo 0 > /sys/kernel/debug/$FAILTYPE/space
336    echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
337    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
338    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
339    echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
340
341    trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
342
343    echo "Injecting errors into the module $module... (interrupt to stop)"
344    sleep 1000000
345
346------------------------------------------------------------------------------
347
348- Inject open_ctree error while btrfs mount::
349
350    #!/bin/bash
351
352    rm -f testfile.img
353    dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
354    DEVICE=$(losetup --show -f testfile.img)
355    mkfs.btrfs -f $DEVICE
356    mkdir -p tmpmnt
357
358    FAILTYPE=fail_function
359    FAILFUNC=open_ctree
360    echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
361    printf %#x -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
362    echo N > /sys/kernel/debug/$FAILTYPE/task-filter
363    echo 100 > /sys/kernel/debug/$FAILTYPE/probability
364    echo 0 > /sys/kernel/debug/$FAILTYPE/interval
365    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
366    echo 0 > /sys/kernel/debug/$FAILTYPE/space
367    echo 1 > /sys/kernel/debug/$FAILTYPE/verbose
368
369    mount -t btrfs $DEVICE tmpmnt
370    if [ $? -ne 0 ]
371    then
372	echo "SUCCESS!"
373    else
374	echo "FAILED!"
375	umount tmpmnt
376    fi
377
378    echo > /sys/kernel/debug/$FAILTYPE/inject
379
380    rmdir tmpmnt
381    losetup -d $DEVICE
382    rm testfile.img
383
384
385Tool to run command with failslab or fail_page_alloc
386----------------------------------------------------
387In order to make it easier to accomplish the tasks mentioned above, we can use
388tools/testing/fault-injection/failcmd.sh.  Please run a command
389"./tools/testing/fault-injection/failcmd.sh --help" for more information and
390see the following examples.
391
392Examples:
393
394Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
395allocation failure::
396
397	# ./tools/testing/fault-injection/failcmd.sh \
398		-- make -C tools/testing/selftests/ run_tests
399
400Same as above except to specify 100 times failures at most instead of one time
401at most by default::
402
403	# ./tools/testing/fault-injection/failcmd.sh --times=100 \
404		-- make -C tools/testing/selftests/ run_tests
405
406Same as above except to inject page allocation failure instead of slab
407allocation failure::
408
409	# env FAILCMD_TYPE=fail_page_alloc \
410		./tools/testing/fault-injection/failcmd.sh --times=100 \
411		-- make -C tools/testing/selftests/ run_tests
412
413Systematic faults using fail-nth
414---------------------------------
415
416The following code systematically faults 0-th, 1-st, 2-nd and so on
417capabilities in the socketpair() system call::
418
419  #include <sys/types.h>
420  #include <sys/stat.h>
421  #include <sys/socket.h>
422  #include <sys/syscall.h>
423  #include <fcntl.h>
424  #include <unistd.h>
425  #include <string.h>
426  #include <stdlib.h>
427  #include <stdio.h>
428  #include <errno.h>
429
430  int main()
431  {
432	int i, err, res, fail_nth, fds[2];
433	char buf[128];
434
435	system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
436	sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
437	fail_nth = open(buf, O_RDWR);
438	for (i = 1;; i++) {
439		sprintf(buf, "%d", i);
440		write(fail_nth, buf, strlen(buf));
441		res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
442		err = errno;
443		pread(fail_nth, buf, sizeof(buf), 0);
444		if (res == 0) {
445			close(fds[0]);
446			close(fds[1]);
447		}
448		printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
449			res, err);
450		if (atoi(buf))
451			break;
452	}
453	return 0;
454  }
455
456An example output::
457
458	1-th fault Y: res=-1/23
459	2-th fault Y: res=-1/23
460	3-th fault Y: res=-1/12
461	4-th fault Y: res=-1/12
462	5-th fault Y: res=-1/23
463	6-th fault Y: res=-1/23
464	7-th fault Y: res=-1/23
465	8-th fault Y: res=-1/12
466	9-th fault Y: res=-1/12
467	10-th fault Y: res=-1/12
468	11-th fault Y: res=-1/12
469	12-th fault Y: res=-1/12
470	13-th fault Y: res=-1/12
471	14-th fault Y: res=-1/12
472	15-th fault Y: res=-1/12
473	16-th fault N: res=0/12
474