2022-09-01 03:13:18

by Li Zhijian

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

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 <[email protected]>
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Li Zhijian <[email protected]>
Reviewed-by: Christian Brauner (Microsoft) <[email protected]>
---
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);
--
1.8.3.1

2022-09-29 01:14:04

by Li Zhijian

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

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 <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Li Zhijian <[email protected]>
> Reviewed-by: Christian Brauner (Microsoft) <[email protected]>
> ---
> 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);

2022-10-30 08:15:42

by Li Zhijian

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 <[email protected]>
>> Reported-by: kernel test robot <[email protected]>
>> Signed-off-by: Li Zhijian <[email protected]>
>> Reviewed-by: Christian Brauner (Microsoft) <[email protected]>
>> ---
>> 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);
>

2022-10-30 08:55:07

by Shuah Khan

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

On 8/31/22 21:10, 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 <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Li Zhijian <[email protected]>
> Reviewed-by: Christian Brauner (Microsoft) <[email protected]>
> ---

Sorry for the delay. Now applied to linux-kselftest fixes for rc4

thanks,
-- Shuah