Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1536117

Re: Unkillable processes due to PTRACE_TRACEME again

Show all headers | View raw

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) {}
?
It seems to work. But want to make sure.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Unkillable processes due to PTRACE_TRACEME again Dmitry Vyukov <dvyukov@google.com> - 2016-12-02 19:50 +0100
  Re: Unkillable processes due to PTRACE_TRACEME again Pavel Machek <pavel@ucw.cz> - 2016-12-02 22:10 +0100
    Re: Unkillable processes due to PTRACE_TRACEME again Dmitry Vyukov <dvyukov@google.com> - 2016-12-03 17:00 +0100
      Re: Unkillable processes due to PTRACE_TRACEME again Pavel Machek <pavel@ucw.cz> - 2016-12-03 20:20 +0100
  Re: Unkillable processes due to PTRACE_TRACEME again Oleg Nesterov <oleg@redhat.com> - 2016-12-05 11:50 +0100
    Re: Unkillable processes due to PTRACE_TRACEME again Oleg Nesterov <oleg@redhat.com> - 2016-12-05 12:10 +0100
      Re: Unkillable processes due to PTRACE_TRACEME again Dmitry Vyukov <dvyukov@google.com> - 2016-12-05 15:10 +0100
        Re: Unkillable processes due to PTRACE_TRACEME again Oleg Nesterov <oleg@redhat.com> - 2016-12-05 18:10 +0100

csiph-web