linux-kernel - Re: [PATCH v3] ksefltests: pidfd: Fix wait

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Message-ID: <b081620b-5a42-82c2-ceba-dcb077e8bd39@fujitsu.com>
Date:   Sun, 30 Oct 2022 16:09:40 +0800
From:   Li Zhijian <lizhijian@...itsu.com>
To:     <brauner@...nel.org>, <shuah@...nel.org>,
        <linux-kselftest@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, Philip Li <philip.li@...el.com>
Subject: Re: [PATCH v3] ksefltests: pidfd: Fix wait_states: Test terminated by
 timeout

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@...el.com>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
>> Reviewed-by: Christian Brauner (Microsoft) <brauner@...nel.org>
>> ---
>> 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);
>