[LTP] [RFC] Shell API timeout sleep orphan processes

[Petr Vorel]

> Hi Petr,
> > > The kill code is not working as expected, because it only kills the shell
> > > process spawned by "sleep $sec && _tst_kill_test &".
> > > We are running single ltp tests using robot framework and robot waits until
> > > all processes of session have finished.
> > Interesting. Do you mean $_tst_setup_timer_pid from _tst_setup_timer was left
> > running if the test does not timeout? Because I was not able to find it.
> Ups there was a bug in my command. Redirection of the output of the test to
> /dev/null does not trigger the long delay:
> Please try with time sh -c './timeout02.sh | cat'
> Sorry for that...

> The line "sleep $sec && _tst_kill_test &" spawns two processes:
> sleep and a shell process, that is (probably) forked from the running shell.
> The pid returned by $! is the pid of this shell.
> When killing the timeout process, only this shell process, but not the sleep
> is killed. That is also were the slowdown comes from.

> However, this might be shell implementation specific. At least for busybox
> sh and I think dash and bash the behavior is the same.

> > Interesting slowdown. It looks to me it's exit $ret in final _tst_do_exit()
> > takes so much time. I have no idea why, but it was here before 25ad54dba
> > ("tst_test.sh: Run cleanup also after test timeout").
> I think what actually is consuming the time is the sleep process, that has
> stdout still opened.
> Redirecting the output of sleep to /dev/null, fixes the hanging, but there
> is still the orphaned sleep process lingering around.
> Try "sleep $sec >/dev/null && _tst_kill_test &"
Indeed, redirection helps. Interesting.

> $ ps; time sh -c 'PATH="$PWD:$PWD/../../../testcases/lib/:$PATH"
> ./timeout02.sh | cat' ; ps
>     PID TTY          TIME CMD
>    2352 pts/5    00:00:00 bash
>   19981 pts/5    00:00:00 ps
> timeout02 1 TINFO: timeout per run is 0h 0m 2s
> timeout02 1 TPASS: timeout 2 set (LTP_TIMEOUT_MUL='1')

> Summary:
> passed   1
> failed   0
> broken   0
> skipped  0
> warnings 0

> real    0m0,013s
> user    0m0,012s
> sys    0m0,005s
>     PID TTY          TIME CMD
>    2352 pts/5    00:00:00 bash
>   19998 pts/5    00:00:00 sleep
>   20001 pts/5    00:00:00 ps
Yep, you're right :(. Thanks a lot for your analysis!

> > > The only way to fix this really portable I can think of is moving the
> > > timeout code (including the logic in _tst_kill_test) into c code. This way
> > > there would only be one binary, that can be killed flawlessly.
> > Maybe set -m would be enough. But sure, rewriting C is usually the best approach
> > for shell problems, we use quite a lot of C helpers for shell already.
> I will send the patch, if this introduces any new issues, we can still
> switch to a c based implementation.
Thank you!

Kind regards,
Petr

> Jörg