Hi!
> > >> waitid(P_ALL, 0, {}, WNOHANG|WEXITED|WSTOPPED|WCONTINUED, NULL) = 0
> > >>
> > >> So what should be fixed here? Kernel of distro init?
> > >
> > > waitpid(__WALL) indeed joins these processes.
>
> Thanks. And I just checked Fedora 22, it doesn't use __WALL too.
>
> So I think we should change the kernel even if this is not a bug...
> I'll send the patch.
>
> > > But __WALL can't be used with waitid and Ubuntu init uses waitid...
>
> Yes, and I never understood why. Perhaps we should change this too.
>
> > #include <pthread.h>
> > #include <unistd.h>
> > #include <sys/ptrace.h>
> > #include <stdio.h>
> > #include <errno.h>
> > #include <signal.h>
> > #include <sys/types.h>
> > #include <sys/wait.h>
> >
> > void *thr(void *arg) {
> > ptrace(PTRACE_TRACEME, 0, 0, 0);
> > return 0;
> > }
> >
> > int main() {
> > int pid = fork();
> > if (pid == 0) {
> > pthread_t th;
> > pthread_create(&th, 0, thr, 0);
> > sleep(1);
> > return 0;
> > }
> > siginfo_t info = {};
> > int status = 0;
> > int res = waitpid(-1, &status, __WALL);
> > printf("pid=%d res=%d errno=%d\n", pid, res, errno);
> > res = waitpid(-1, &status, __WALL);
> > printf("pid=%d res=%d errno=%d\n", pid, res, errno);
> > return 0;
> > }
> >
> >
> > However, I need to wait for a particular child and if I change the
> > first waitpid to:
> >
> > int res = waitpid(pid, &status, __WALL);
> >
> > then it does not terminate.
> > So how can I wait for such child process?
>
> You can't. This is one of historical oddities. You need to reap the
> traced sub-thread first. And PTRACE_DETACH doesn't work.
If kill -9 does not take out the process, surely that sounds like a
security problem?
I know ptrace is old and tricky and ugly, but ....?
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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