On Tue, Jul 9, 2024 at 2:43 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > Hi Kir, > > On 07/08, Kir Kolyshkin wrote: > > > > [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=64bef697d33b > > The changelog says: > > pidfd: implement PIDFD_THREAD flag for pidfd_open() > > With this flag: > > - pidfd_open() doesn't require that the target task must be > a thread-group leader > > - pidfd_poll() succeeds when the task exits and becomes a > zombie (iow, passes exit_notify()), even if it is a leader > and thread-group is not empty. > > This means that the behaviour of pidfd_poll(PIDFD_THREAD, > pid-of-group-leader) is not well defined if it races with > exec() from its sub-thread; pidfd_poll() can succeed or not > depending on whether pidfd_task_exited() is called before > or after exchange_tids(). > > > +The behavior depends on whether the file descriptor refers > > +to a process (thread-group leader) or a thread (see > > +.B PIDFD_THREAD > > +above): > > +.RS > > +.IP \[bu] 3 > > +For a thread-group leader, the polling task is woken if the > > +thread-group is empty. In other words, if the thread-group > > +leader task exits when there are still threads alive in its > > +thread-group, the polling task will not be woken when the > > +thread-group leader exits, but rather when the last thread in the > > +thread-group exits. > > so this part is not accurate. I copied the above text almost verbatim from the merge commit description (commit b5683a37c881). Until it's clarified, let's remove this text, adding a TODO instead. > > See also 43f0df54c96fa5a ("pidfd_poll: report POLLHUP when pid_task() == NULL") > which adds another feature. > > Oleg. >
