Re: [PATCH v3] ksefltests: pidfd: Fix wait_states: Test terminated by timeout

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ping again


On 29/09/2022 08:56, Li Zhijian wrote:
ping


On 01/09/2022 11:10, Li Zhijian 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 goes first, the test will fail.

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@xxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
---
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.
V3: fixes description and add review tag
V2: rewrite with pipe to avoid usleep
---
  tools/testing/selftests/pidfd/pidfd_wait.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
index 070c1c876df1..c3e2a3041f55 100644
--- a/tools/testing/selftests/pidfd/pidfd_wait.c
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -95,20 +95,28 @@ static int sys_waitid(int which, pid_t pid, siginfo_t *info, int options,
          .flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
          .exit_signal = SIGCHLD,
      };
+    int 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 +125,8 @@ static int sys_waitid(int which, pid_t pid, siginfo_t *info, int options,
      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);





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