On 12/05, Dmitry Vyukov wrote:
>
> On Mon, Dec 5, 2016 at 12:00 PM, Oleg Nesterov <o...@redhat.com> wrote:
> > On 12/05, Oleg Nesterov wrote:
> >>
> >> On 12/02, Dmitry Vyukov wrote:
> >> >
> >> > I am not on 2caceb3294a78c389b462e7e236a4e744a53a474 (Dec 1). And see
> >> > the same unwaitable zombie processes.
> >>
> >> This is another thing, and notabug. This is how ptrace works,
> >>
> >> > void *thr(void *arg)
> >> > {
> >> > ptrace(PTRACE_TRACEME, 0, 0, 0);
> >> > }
> >> >
> >> > int main()
> >> > {
> >> > int pid = fork();
> >> > if (pid == 0) {
> >> > pthread_t th;
> >> > pthread_create(&th, 0, thr, 0);
> >> > usleep(100000);
> >> > exit(0);
> >> > }
> >> > usleep(200000);
> >> > kill(pid, SIGKILL);
> >> > int status = 0;
> >> > waitpid(pid, &status, __WALL);
> >>
> >> waitpid(pid) hangs because you need to reap the sub-thread first.
> >
> > I'm afraid I wasn't clear...
> >
> > So the child process has 2 threads, the leader thread L and the sub-thread
> > T.
> > waitpid(pid == L->pid) will block until all the threads go away, but since
> > T is
> > traced it won't autoreap, the tracer should do waitpid(T->pid) first to reap
> > this zombie. waitpid(-1) should work too.
>
> Do you mean that I need to replace:
> waitpid(pid, &status, __WALL);
> with:
> while (waitpid(-1, &status, __WALL) != pid) {}
> ?
Yes. Or, if you knew the pid of the traced thread you could do
// need to do this first, the traced sub-thread won't autoreap,
// and the leader which represents the whole process is not reapable
// until all other threads go away
waitpid(tracee_pid, &status, __WALL);
waitpid(pid, &status, __WALL);
Oleg.
