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-rw-r--r--Documentation/fault-injection/fault-injection.txt78
-rw-r--r--fs/proc/base.c52
-rw-r--r--include/linux/sched.h1
-rw-r--r--kernel/fork.c4
-rw-r--r--lib/fault-inject.c7
5 files changed, 142 insertions, 0 deletions
diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
index 415484f..192d8cb 100644
--- a/Documentation/fault-injection/fault-injection.txt
+++ b/Documentation/fault-injection/fault-injection.txt
@@ -134,6 +134,22 @@ use the boot option:
fail_futex=
mmc_core.fail_request=<interval>,<probability>,<space>,<times>
+o proc entries
+
+- /proc/self/task/<current-tid>/fail-nth:
+
+ Write to this file of integer N makes N-th call in the current task fail
+ (N is 0-based). Read from this file returns a single char 'Y' or 'N'
+ that says if the fault setup with a previous write to this file was
+ injected or not, and disables the fault if it 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 +294,65 @@ 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 = 0;; i++) {
+ sprintf(buf, "%d", i);
+ write(fail_nth, buf, strlen(buf));
+ res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
+ err = errno;
+ read(fail_nth, buf, 1);
+ if (res == 0) {
+ close(fds[0]);
+ close(fds[1]);
+ }
+ printf("%d-th fault %c: res=%d/%d\n", i, buf[0], res, err);
+ if (buf[0] != 'Y')
+ break;
+ }
+ return 0;
+}
+
+An example output:
+
+0-th fault Y: res=-1/23
+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
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f1e1927..88b773f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1355,6 +1355,53 @@ static const struct file_operations proc_fault_inject_operations = {
.write = proc_fault_inject_write,
.llseek = generic_file_llseek,
};
+
+static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct task_struct *task;
+ int err, n;
+
+ task = get_proc_task(file_inode(file));
+ if (!task)
+ return -ESRCH;
+ put_task_struct(task);
+ if (task != current)
+ return -EPERM;
+ err = kstrtoint_from_user(buf, count, 10, &n);
+ if (err)
+ return err;
+ if (n < 0 || n == INT_MAX)
+ return -EINVAL;
+ current->fail_nth = n + 1;
+ return count;
+}
+
+static ssize_t proc_fail_nth_read(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct task_struct *task;
+ int err;
+
+ task = get_proc_task(file_inode(file));
+ if (!task)
+ return -ESRCH;
+ put_task_struct(task);
+ if (task != current)
+ return -EPERM;
+ if (count < 1)
+ return -EINVAL;
+ err = put_user((char)(current->fail_nth ? 'N' : 'Y'), buf);
+ if (err)
+ return err;
+ current->fail_nth = 0;
+ return 1;
+}
+
+static const struct file_operations proc_fail_nth_operations = {
+ .read = proc_fail_nth_read,
+ .write = proc_fail_nth_write,
+};
#endif
@@ -3311,6 +3358,11 @@ static const struct pid_entry tid_base_stuff[] = {
#endif
#ifdef CONFIG_FAULT_INJECTION
REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
+ /*
+ * Operations on the file check that the task is current,
+ * so we create it with 0666 to support testing under unprivileged user.
+ */
+ REG("fail-nth", 0666, proc_fail_nth_operations),
#endif
#ifdef CONFIG_TASK_IO_ACCOUNTING
ONE("io", S_IRUSR, proc_tid_io_accounting),
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 20814b7..3822d74 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -974,6 +974,7 @@ struct task_struct {
#ifdef CONFIG_FAULT_INJECTION
int make_it_fail;
+ int fail_nth;
#endif
/*
* When (nr_dirtied >= nr_dirtied_pause), it's time to call
diff --git a/kernel/fork.c b/kernel/fork.c
index d2b9d7c..ade237a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -573,6 +573,10 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
kcov_task_init(tsk);
+#ifdef CONFIG_FAULT_INJECTION
+ tsk->fail_nth = 0;
+#endif
+
return tsk;
free_stack:
diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index 4ff1571..09ac73c1 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -107,6 +107,12 @@ static inline bool fail_stacktrace(struct fault_attr *attr)
bool should_fail(struct fault_attr *attr, ssize_t size)
{
+ if (in_task() && current->fail_nth) {
+ if (--current->fail_nth == 0)
+ goto fail;
+ return false;
+ }
+
/* No need to check any other properties if the probability is 0 */
if (attr->probability == 0)
return false;
@@ -134,6 +140,7 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
if (!fail_stacktrace(attr))
return false;
+fail:
fail_dump(attr);
if (atomic_read(&attr->times) != -1)
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