summaryrefslogtreecommitdiffstats
path: root/Documentation/fault-injection/fault-injection.txt
blob: b7ca560b93407ca94848ced9304a52b2365c9559 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
Fault injection capabilities infrastructure
===========================================

See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.


Available fault injection capabilities
--------------------------------------

o failslab

  injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)

o fail_page_alloc

  injects page allocation failures. (alloc_pages(), get_free_pages(), ...)

o fail_make_request

  injects disk IO errors on devices permitted by setting
  /sys/block/<device>/make-it-fail or
  /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())

Configure fault-injection capabilities behavior
-----------------------------------------------

o debugfs entries

fault-inject-debugfs kernel module provides some debugfs entries for runtime
configuration of fault-injection capabilities.

- /debug/fail*/probability:

	likelihood of failure injection, in percent.
	Format: <percent>

	Note that one-failure-per-hundred is a very high error rate
	for some testcases.  Consider setting probability=100 and configure
	/debug/fail*/interval for such testcases.

- /debug/fail*/interval:

	specifies the interval between failures, for calls to
	should_fail() that pass all the other tests.

	Note that if you enable this, by setting interval>1, you will
	probably want to set probability=100.

- /debug/fail*/times:

	specifies how many times failures may happen at most.
	A value of -1 means "no limit".

- /debug/fail*/space:

	specifies an initial resource "budget", decremented by "size"
	on each call to should_fail(,size).  Failure injection is
	suppressed until "space" reaches zero.

- /debug/fail*/verbose

	Format: { 0 | 1 | 2 }
	specifies the verbosity of the messages when failure is
	injected.  '0' means no messages; '1' will print only a single
	log line per failure; '2' will print a call trace too -- useful
	to debug the problems revealed by fault injection.

- /debug/fail*/task-filter:

	Format: { 'Y' | 'N' }
	A value of 'N' disables filtering by process (default).
	Any positive value limits failures to only processes indicated by
	/proc/<pid>/make-it-fail==1.

- /debug/fail*/require-start:
- /debug/fail*/require-end:
- /debug/fail*/reject-start:
- /debug/fail*/reject-end:

	specifies the range of virtual addresses tested during
	stacktrace walking.  Failure is injected only if some caller
	in the walked stacktrace lies within the required range, and
	none lies within the rejected range.
	Default required range is [0,ULONG_MAX) (whole of virtual address space).
	Default rejected range is [0,0).

- /debug/fail*/stacktrace-depth:

	specifies the maximum stacktrace depth walked during search
	for a caller within [require-start,require-end) OR
	[reject-start,reject-end).

- /debug/fail_page_alloc/ignore-gfp-highmem:

	Format: { 'Y' | 'N' }
	default is 'N', setting it to 'Y' won't inject failures into
	highmem/user allocations.

- /debug/failslab/ignore-gfp-wait:
- /debug/fail_page_alloc/ignore-gfp-wait:

	Format: { 'Y' | 'N' }
	default is 'N', setting it to 'Y' will inject failures
	only into non-sleep allocations (GFP_ATOMIC allocations).

o Boot option

In order to inject faults while debugfs is not available (early boot time),
use the boot option:

	failslab=
	fail_page_alloc=
	fail_make_request=<interval>,<probability>,<space>,<times>

How to add new fault injection capability
-----------------------------------------

o #include <linux/fault-inject.h>

o define the fault attributes

  DECLARE_FAULT_INJECTION(name);

  Please see the definition of struct fault_attr in fault-inject.h
  for details.

o provide a way to configure fault attributes

- boot option

  If you need to enable the fault injection capability from boot time, you can
  provide boot option to configure it. There is a helper function for it:

	setup_fault_attr(attr, str);

- debugfs entries

  failslab, fail_page_alloc, and fail_make_request use this way.
  Helper functions:

	init_fault_attr_entries(entries, attr, name);
	void cleanup_fault_attr_entries(entries);

- module parameters

  If the scope of the fault injection capability is limited to a
  single kernel module, it is better to provide module parameters to
  configure the fault attributes.

o add a hook to insert failures

  Upon should_fail() returning true, client code should inject a failure.

	should_fail(attr, size);

Application Examples
--------------------

o inject slab allocation failures into module init/cleanup code

------------------------------------------------------------------------------
#!/bin/bash

FAILCMD=Documentation/fault-injection/failcmd.sh
BLACKLIST="root_plug evbug"

FAILNAME=failslab
echo Y > /debug/$FAILNAME/task-filter
echo 10 > /debug/$FAILNAME/probability
echo 100 > /debug/$FAILNAME/interval
echo -1 > /debug/$FAILNAME/times
echo 2 > /debug/$FAILNAME/verbose
echo 1 > /debug/$FAILNAME/ignore-gfp-wait

blacklist()
{
	echo $BLACKLIST | grep $1 > /dev/null 2>&1
}

oops()
{
	dmesg | grep BUG > /dev/null 2>&1
}

find /lib/modules/`uname -r` -name '*.ko' -exec basename {} .ko \; |
	while read i
	do
		oops && exit 1

		if ! blacklist $i
		then
			echo inserting $i...
			bash $FAILCMD modprobe $i
		fi
	done

lsmod | awk '{ if ($3 == 0) { print $1 } }' |
	while read i
	do
		oops && exit 1

		if ! blacklist $i
		then
			echo removing $i...
			bash $FAILCMD modprobe -r $i
		fi
	done

------------------------------------------------------------------------------

o inject slab allocation failures only for a specific module

------------------------------------------------------------------------------
#!/bin/bash

FAILMOD=Documentation/fault-injection/failmodule.sh

echo injecting errors into the module $1...

modprobe $1
bash $FAILMOD failslab $1 10
echo 25 > /debug/failslab/probability

------------------------------------------------------------------------------