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Diffstat (limited to 'Documentation/fault-injection/fault-injection.txt')
| -rw-r--r-- | Documentation/fault-injection/fault-injection.txt | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt index 415484f3d59a..918972babcd8 100644 --- a/Documentation/fault-injection/fault-injection.txt +++ b/Documentation/fault-injection/fault-injection.txt @@ -134,6 +134,23 @@ use the boot option: fail_futex= mmc_core.fail_request=<interval>,<probability>,<space>,<times> +o proc entries + +- /proc/<pid>/fail-nth: +- /proc/self/task/<tid>/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 ----------------------------------------- @@ -278,3 +295,65 @@ 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 |