On 18/07/2022 10:58, Li, Zhijian/李 智坚 wrote:

0Day/LKP observed that the kselftest blocks forever 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);

wait_states has below testing flow: CHILD PARENT ---------------+-------------- 1 STOP itself 2 WAIT for CHILD STOPPED 3 SIGNAL CHILD to CONT 4 CONT 5 STOP itself 5' WAIT for CHILD CONT 6 WAIT for CHILD STOPPED

The problem is that the kernel cannot ensure the order of 5 and 5', once 5's goes first, the test will fail.

Correct: s/once 5's goes first/once 5 goes first

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 philip.li@intel.com Reported-by: kernel test robot lkp@intel.com Signed-off-by: Li Zhijian lizhijian@fujitsu.com

---

I have almost forgotten this patch since the former version post over 6 months ago. This time I just do a rebase and update the comments. V2: rewrite with pipe to avoid usleep

---

tools/testing/selftests/pidfd/pidfd_wait.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c index 070c1c876df1..3f7bc6517dea 100644 --- a/tools/testing/selftests/pidfd/pidfd_wait.c +++ b/tools/testing/selftests/pidfd/pidfd_wait.c @@ -95,20 +95,27 @@ TEST(wait_states) .flags = CLONE_PIDFD | CLONE_PARENT_SETTID, .exit_signal = SIGCHLD, };

• 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);

@@ -117,6 +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);