On 01/25, Christian Brauner wrote: > > > > When it is reaped is "mostly unrelated". > > > > Then why pidfd_poll() can't simply check !task || task->exit_state ? > > > > Nevermind. So, currently pidfd_poll() succeeds when the leader can be > > Hm, the comment right above mentions: > > /* > * Inform pollers only when the whole thread group exits. > * If the thread group leader exits before all other threads in the > * group, then poll(2) should block, similar to the wait(2) family. > */ > > reaped, iow the whole thread group has exited. Yes, but the comment doesn't contradict with what I have said? > > But even if you are the > > parent, you can't expect that wait(WNOHANG) must succeed, the leader > > can be traced. I guess it is too late to change this behaviour. > > Hm, why is that an issue though? Well, I didn't say this is a problem. I simply do not know how/why people use pidfd_poll(). I mostly tried to explain why do I think that do_notify_pidfd() should be always called from exit_notify() path, not by release_task(), even if the task is not a leader. > Because a program would rely on WNOHANG to hang on > a ptraced leader? That seems esoteric imho. To me it would be usefule, but lets not discuss this now. The "patch" I sent doesn't change the current behaviour. > > What if we add the new PIDFD_THREAD flag? With this flag > > > > - sys_pidfd_open() doesn't require the must be a group leader > > Yes. > > > > > - pidfd_poll() succeeds when the task passes exit_notify() and > > becomes a zombie, even if it is a leader and has other threads. > > Iiuc, if an existing user creates a pidfd for a thread-group leader and > then polls that pidfd they would currently only get notified if the > thread-group is empty and the leader has exited. > > If we now start notifying when the thread-group leader exits but the > thread-group isn't empty then this would be a fairly big api change Hmm... again, this patch doesn't (shouldn't) change the current behavior. Please note "with this flag" above. If sys_pidfd_open() was called without PIDFD_THREAD, then sys_pidfd_open() still requires that the target task must be a group leader, and pidfd_poll() won't succeed until the leader exits and thread_group_empty() is true. Oleg.
