Messages in this thread | | | Date | Mon, 5 Dec 2016 12:00:17 +0100 | From | Oleg Nesterov <> | Subject | Re: Unkillable processes due to PTRACE_TRACEME again |
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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.
Oleg.
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