Root/Documentation/fault-injection/fault-injection.txt

1Fault injection capabilities infrastructure
2===========================================
3
4See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
5
6
7Available fault injection capabilities
8--------------------------------------
9
10o failslab
11
12  injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
13
14o fail_page_alloc
15
16  injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
17
18o 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
24Configure fault-injection capabilities behavior
25-----------------------------------------------
26
27o debugfs entries
28
29fault-inject-debugfs kernel module provides some debugfs entries for runtime
30configuration 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
111o Boot option
112
113In order to inject faults while debugfs is not available (early boot time),
114use the boot option:
115
116    failslab=
117    fail_page_alloc=
118    fail_make_request=<interval>,<probability>,<space>,<times>
119
120How to add new fault injection capability
121-----------------------------------------
122
123o #include <linux/fault-inject.h>
124
125o 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
132o 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
154o 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
160Application Examples
161--------------------
162
163o Inject slab allocation failures into module init/exit code
164
165#!/bin/bash
166
167FAILTYPE=failslab
168echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
169echo 10 > /sys/kernel/debug/$FAILTYPE/probability
170echo 100 > /sys/kernel/debug/$FAILTYPE/interval
171echo -1 > /sys/kernel/debug/$FAILTYPE/times
172echo 0 > /sys/kernel/debug/$FAILTYPE/space
173echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
174echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
175
176faulty_system()
177{
178    bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
179}
180
181if [ $# -eq 0 ]
182then
183    echo "Usage: $0 modulename [ modulename ... ]"
184    exit 1
185fi
186
187for m in $*
188do
189    echo inserting $m...
190    faulty_system modprobe $m
191
192    echo removing $m...
193    faulty_system modprobe -r $m
194done
195
196------------------------------------------------------------------------------
197
198o Inject page allocation failures only for a specific module
199
200#!/bin/bash
201
202FAILTYPE=fail_page_alloc
203module=$1
204
205if [ -z $module ]
206then
207    echo "Usage: $0 <modulename>"
208    exit 1
209fi
210
211modprobe $module
212
213if [ ! -d /sys/module/$module/sections ]
214then
215    echo Module $module is not loaded
216    exit 1
217fi
218
219cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
220cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
221
222echo N > /sys/kernel/debug/$FAILTYPE/task-filter
223echo 10 > /sys/kernel/debug/$FAILTYPE/probability
224echo 100 > /sys/kernel/debug/$FAILTYPE/interval
225echo -1 > /sys/kernel/debug/$FAILTYPE/times
226echo 0 > /sys/kernel/debug/$FAILTYPE/space
227echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
228echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
229echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
230echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
231
232trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
233
234echo "Injecting errors into the module $module... (interrupt to stop)"
235sleep 1000000
236
237

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