Messages in this thread | | | Date | Mon, 5 Dec 2016 17:59:58 +0100 | From | Oleg Nesterov <> | Subject | Re: Unkillable processes due to PTRACE_TRACEME again |
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On 12/05, Dmitry Vyukov wrote: > > On Mon, Dec 5, 2016 at 12:00 PM, Oleg Nesterov <oleg@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.
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