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

[Li Zhijian]

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);