Re: [PATCH mptcp-next 1/4] selftests: mptcp: join: properly kill background tasks

[Matthieu Baerts <matttbe@kernel.org>]

Hi Geliang,

Thank you for the reviews.

11 Nov 2025 03:46:06 Geliang Tang <geliang@kernel.org>:

> Hi Matt,
>
> This for this fix.
>
> On Sat, 2025-11-08 at 15:20 +0100, Matthieu Baerts (NGI0) wrote:
>> The 'run_tests' function is executed in the background, but killing
>> its
>> associated PID would not kill the children tasks running in the
>> background.
>>
>> To properly kill all background tasks, 'kill -- -PID' could be used,
>> but
>> this requires kill from procps-ng. Instead, all children tasks are
>> listed using 'ps', and 'kill' is called with all PIDs of this group.

(...)

>> diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> index ce6c92826be7..91ec75ddcb96 100644
>> --- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> +++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> @@ -359,6 +359,27 @@ mptcp_lib_kill_wait() {
>>     wait "${1}" 2>/dev/null
>>  }
>>  
>> +# $1: PID
>> +mptcp_lib_pid_list_children() {
>> +   local curr="${1}"
>> +   # evoke 'ps' only once
>> +   local pids="${2:-"$(ps o pid,ppid)"}"
>> +
>> +   echo "${curr}"
>> +
>> +   local pid
>> +   for pid in $(echo "${pids}" | awk "\$2 == ${curr} { print
>> \$1 }"); do
>> +       mptcp_lib_pid_list_children "${pid}" "${pids}"
>
> To be honest, I don't understand why this mptcp_lib_pid_list_children
> function is calling itself here. Is this recursion?

Yes it is a recursion: children processes can have children ones.

mptcp_lib_pid_list_children() will print the PID it is called with, and call
itself with all children (can be none).

In our case with mptcp_join.sh, it means getting the run_tests job plus
the other background tasks: mptcp_connect (x2), the timeout, and
eventually the task modifying the endpoints.

Cheers,
Matt