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