Kernel-4.18.0-80.el8_fault-injection

Fault injection capabilities infrastructure

See also drivers/md/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_futex

injects futex deadlock and uaddr fault errors.

o fail_make_request

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

o fail_mmc_request

injects MMC data errors on devices permitted by setting
debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request

o fail_function

injects error return on specific functions, which are marked by
ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
under /sys/kernel/debug/fail_function. No boot option supported.

o NVMe fault injection

inject NVMe status code and retry flag on devices permitted by setting
debugfs entries under /sys/kernel/debug/nvme*/fault_inject. The default
status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
retry flag can be set via the debugfs.

Configure fault-injection capabilities behavior

o debugfs entries

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

• /sys/kernel/debug/fail*/probability:

  likelihood of failure injection, in percent.
  Format:

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

• /sys/kernel/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.

• /sys/kernel/debug/fail*/times:

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

• /sys/kernel/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.

• /sys/kernel/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.

• /sys/kernel/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//make-it-fail==1.

• /sys/kernel/debug/fail*/require-start:

• /sys/kernel/debug/fail*/require-end:

• /sys/kernel/debug/fail*/reject-start:

• /sys/kernel/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).

• /sys/kernel/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).

• /sys/kernel/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.

• /sys/kernel/debug/failslab/ignore-gfp-wait:

• /sys/kernel/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).

• /sys/kernel/debug/fail_page_alloc/min-order:

  specifies the minimum page allocation order to be injected
  failures.

• /sys/kernel/debug/fail_futex/ignore-private:

  Format: { ‘Y’ | ‘N’ }
  default is ‘N’, setting it to ‘Y’ will disable failure injections
  when dealing with private (address space) futexes.

• /sys/kernel/debug/fail_function/inject:

  Format: { ‘function-name’ | ‘!function-name’ | ‘’ }
  specifies the target function of error injection by name.
  If the function name leads ‘!’ prefix, given function is
  removed from injection list. If nothing specified (‘’)
  injection list is cleared.

• /sys/kernel/debug/fail_function/injectable:

  (read only) shows error injectable functions and what type of
  error values can be specified. The error type will be one of
  below;

  • NULL: retval must be 0.
  • ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
  • ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).

• /sys/kernel/debug/fail_function//retval:

  specifies the “error” return value to inject to the given
  function for given function. This will be created when
  user specifies new injection entry.

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=
fail_futex=
mmc_core.fail_request=<interval>,<probability>,<space>,<times>

o proc entries

• /proc//fail-nth:

• /proc/self/task//fail-nth:

  Write to this file of integer N makes N-th call in the task fail.
  Read from this file returns a integer value. A value of ‘0’ indicates
  that the fault setup with a previous write to this file was injected.
  A positive integer N indicates that the fault wasn’t yet injected.
  Note that this file enables all types of faults (slab, futex, etc).
  This setting takes precedence over all other generic debugfs settings
  like probability, interval, times, etc. But per-capability settings
  (e.g. fail_futex/ignore-private) take precedence over it.

  This feature is intended for systematic testing of faults in a single
  system call. See an example below.

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:

  fault_create_debugfs_attr(name, parent, attr);

• 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/exit code

#!/bin/bash

FAILTYPE=failslab
echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
echo 10 > /sys/kernel/debug/$FAILTYPE/probability
echo 100 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait

faulty_system()
{
bash -c “echo 1 > /proc/self/make-it-fail && exec $*”
}

if [ $# -eq 0 ]
then
echo “Usage: $0 modulename [ modulename … ]”
exit 1
fi

for m in $*
do
echo inserting $m…
faulty_system modprobe $m

echo removing $m...
faulty_system modprobe -r $m

done

---

o Inject page allocation failures only for a specific module

#!/bin/bash

FAILTYPE=fail_page_alloc
module=$1

if [ -z $module ]
then
echo “Usage: $0 “
exit 1
fi

modprobe $module

if [ ! -d /sys/module/$module/sections ]
then
echo Module $module is not loaded
exit 1
fi

cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end

echo N > /sys/kernel/debug/$FAILTYPE/task-filter
echo 10 > /sys/kernel/debug/$FAILTYPE/probability
echo 100 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth

trap “echo 0 > /sys/kernel/debug/$FAILTYPE/probability” SIGINT SIGTERM EXIT

echo “Injecting errors into the module $module… (interrupt to stop)”
sleep 1000000

---

o Inject open_ctree error while btrfs mount

#!/bin/bash

rm -f testfile.img
dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
DEVICE=$(losetup –show -f testfile.img)
mkfs.btrfs -f $DEVICE
mkdir -p tmpmnt

FAILTYPE=fail_function
FAILFUNC=open_ctree
echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
echo -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
echo N > /sys/kernel/debug/$FAILTYPE/task-filter
echo 100 > /sys/kernel/debug/$FAILTYPE/probability
echo 0 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 1 > /sys/kernel/debug/$FAILTYPE/verbose

mount -t btrfs $DEVICE tmpmnt
if [ $? -ne 0 ]
then
echo “SUCCESS!”
else
echo “FAILED!”
umount tmpmnt
fi

echo > /sys/kernel/debug/$FAILTYPE/inject

rmdir tmpmnt
losetup -d $DEVICE
rm testfile.img

Tool to run command with failslab or fail_page_alloc

In order to make it easier to accomplish the tasks mentioned above, we can use
tools/testing/fault-injection/failcmd.sh. Please run a command
“./tools/testing/fault-injection/failcmd.sh –help” for more information and
see the following examples.

Examples:

Run a command “make -C tools/testing/selftests/ run_tests” with injecting slab
allocation failure.

# ./tools/testing/fault-injection/failcmd.sh \
    -- make -C tools/testing/selftests/ run_tests

Same as above except to specify 100 times failures at most instead of one time
at most by default.

# ./tools/testing/fault-injection/failcmd.sh --times=100 \
    -- make -C tools/testing/selftests/ run_tests

Same as above except to inject page allocation failure instead of slab
allocation failure.

# env FAILCMD_TYPE=fail_page_alloc \
    ./tools/testing/fault-injection/failcmd.sh --times=100 \
            -- make -C tools/testing/selftests/ run_tests

Systematic faults using fail-nth

The following code systematically faults 0-th, 1-st, 2-nd and so on
capabilities in the socketpair() system call.

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>

int main()
{
int i, err, res, fail_nth, fds[2];
char buf[128];

system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
fail_nth = open(buf, O_RDWR);
for (i = 1;; i++) {
    sprintf(buf, "%d", i);
    write(fail_nth, buf, strlen(buf));
    res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
    err = errno;
    pread(fail_nth, buf, sizeof(buf), 0);
    if (res == 0) {
        close(fds[0]);
        close(fds[1]);
    }
    printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
        res, err);
    if (atoi(buf))
        break;
}
return 0;

}

An example output:

1-th fault Y: res=-1/23
2-th fault Y: res=-1/23
3-th fault Y: res=-1/12
4-th fault Y: res=-1/12
5-th fault Y: res=-1/23
6-th fault Y: res=-1/23
7-th fault Y: res=-1/23
8-th fault Y: res=-1/12
9-th fault Y: res=-1/12
10-th fault Y: res=-1/12
11-th fault Y: res=-1/12
12-th fault Y: res=-1/12
13-th fault Y: res=-1/12
14-th fault Y: res=-1/12
15-th fault Y: res=-1/12
16-th fault N: res=0/12