2021-12-17 09:31:29

by Li Zhijian

Subject: [PATCH v2] ksefltest: pidfd: Fix wait_states: Test terminated by timeout

0Day/LKP observed that the kselftest blocks foever since one of the
pidfd_wait doesn't terminate in 1 of 30 runs. After digging into
the source, we found that it blocks at:
ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);

we can reproduce it by:
$ while true; do make run_tests -C pidfd; done

Introduce a blocking read in child process to make sure the parent can
check its WCONTINUED.

CC: Philip Li <[email protected]>
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Li Zhijian <[email protected]>
---
V2: rewrite with pipe to avoid usleep
---
tools/testing/selftests/pidfd/pidfd_wait.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
index be2943f072f6..d5c0ffa26c32 100644
--- a/tools/testing/selftests/pidfd/pidfd_wait.c
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -96,21 +96,26 @@ TEST(wait_states)
.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
.exit_signal = SIGCHLD,
};
- int ret;
+ int ret, pfd[2];
pid_t pid;
siginfo_t info = {
.si_signo = 0,
};
-
+ ASSERT_EQ(pipe(pfd), 0);
pid = sys_clone3(&args);
ASSERT_GE(pid, 0);

if (pid == 0) {
+ char buf[2];
+ close(pfd[1]);
kill(getpid(), SIGSTOP);
+ ASSERT_EQ(read(pfd[0], buf, 1), 1);
+ close(pfd[0]);
kill(getpid(), SIGSTOP);
exit(EXIT_SUCCESS);
}

+ close(pfd[0]);
ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL), 0);
ASSERT_EQ(info.si_signo, SIGCHLD);
ASSERT_EQ(info.si_code, CLD_STOPPED);
@@ -119,6 +124,8 @@ TEST(wait_states)
ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0);

ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);
+ ASSERT_EQ(write(pfd[1], "C", 1), 1);
+ close(pfd[1]);
ASSERT_EQ(info.si_signo, SIGCHLD);
ASSERT_EQ(info.si_code, CLD_CONTINUED);
ASSERT_EQ(info.si_pid, parent_tid);
--
2.33.0

2022-01-13 05:58:51

by Zhijian Li (Fujitsu)

Subject: Re: [PATCH v2] ksefltest: pidfd: Fix wait_states: Test terminated by timeout

ping


On 17/12/2021 17:30, Li Zhijian wrote:
> 0Day/LKP observed that the kselftest blocks foever since one of the
> pidfd_wait doesn't terminate in 1 of 30 runs. After digging into
> the source, we found that it blocks at:
> ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);
>
> we can reproduce it by:
> $ while true; do make run_tests -C pidfd; done
>
> Introduce a blocking read in child process to make sure the parent can
> check its WCONTINUED.
>
> CC: Philip Li <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Li Zhijian <[email protected]>
> ---
> V2: rewrite with pipe to avoid usleep
> ---
> tools/testing/selftests/pidfd/pidfd_wait.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
> index be2943f072f6..d5c0ffa26c32 100644
> --- a/tools/testing/selftests/pidfd/pidfd_wait.c
> +++ b/tools/testing/selftests/pidfd/pidfd_wait.c
> @@ -96,21 +96,26 @@ TEST(wait_states)
> .flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
> .exit_signal = SIGCHLD,
> };
> - int ret;
> + int ret, pfd[2];
> pid_t pid;
> siginfo_t info = {
> .si_signo = 0,
> };
> -
> + ASSERT_EQ(pipe(pfd), 0);
> pid = sys_clone3(&args);
> ASSERT_GE(pid, 0);
>
> if (pid == 0) {
> + char buf[2];
> + close(pfd[1]);
> kill(getpid(), SIGSTOP);
> + ASSERT_EQ(read(pfd[0], buf, 1), 1);
> + close(pfd[0]);
> kill(getpid(), SIGSTOP);
> exit(EXIT_SUCCESS);
> }
>
> + close(pfd[0]);
> ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL), 0);
> ASSERT_EQ(info.si_signo, SIGCHLD);
> ASSERT_EQ(info.si_code, CLD_STOPPED);
> @@ -119,6 +124,8 @@ TEST(wait_states)
> ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0);
>
> ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);
> + ASSERT_EQ(write(pfd[1], "C", 1), 1);
> + close(pfd[1]);
> ASSERT_EQ(info.si_signo, SIGCHLD);
> ASSERT_EQ(info.si_code, CLD_CONTINUED);
> ASSERT_EQ(info.si_pid, parent_tid);