Re: [PATCH v3 2/6] posix-cpu-timers: Use PIDTYPE_TGID to simplify the logic in lookup_task

Oleg Nesterov
2020-04-28T18:03:32Z

On 04/27, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > Eric,
> >
> > I am sick today and can't read the code, but I feel this patch is not
> > right ... please correct me.
>
>
> > So, iiuc when posix_cpu_timer_create() is called and CPUCLOCK_PERTHREAD
> > is false we roughly have
> >
> > task = pid_task(pid, PIDTYPE_TGID); // lookup_task()
> >
> > /* WINDOW */
> >
> > timer->it.cpu.pid = = get_task_pid(task, PIDTYPE_TGID) // posix_cpu_timer_create()
> >
> > Now suppose that we race with mt-exec and this "task" is the old leader;
> > it can be release_task()'ed in the WINDOW above and then get_task_pid()
> > will return NULL.
>
> Except it is asking for PIDTYPE_TGID.
>
> task->signal

Ah yes, I knew I missed something...

Oleg.