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@intel.com Reported-by: kernel test robot lkp@intel.com Signed-off-by: Li Zhijian lizhijian@fujitsu.com Reviewed-by: Christian Brauner (Microsoft) brauner@kernel.org

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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

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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);