Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd

On 03/14, Josh Triplett wrote:

What I was proposing was that a task that isn't yet dead, but that is
going to be autoreaped, is not eligible for waiting either.  All the
various wait* familiy of system calls should pretend it doesn't exist at
all, because returning an autoreaped task from a wait* call introduces a
race condition if the parent tries to *do* anything with the returned
PID.  If you launch a process with CLONE_FD, you need to manage it
exclusively with that fd, not with the wait* family of system calls.

That also implies that the child-stop and child-continued mechanisms
(do_notify_parent_cldstop, WSTOPPED, WCONTINUED) should ignore the task
too.  In the future there could be a flag to clone4 that lets you get
stop and continue notifications through the file descriptor.

So far I strongly disagree, and I think that "autoreap" feature should
not depend on CLONE_FD.

However, as I already said, perhaps something like W_IGNORE_AUTOREAP
for wait* makes sense.

Plus we should also discuss the reparenting. Ok, let me leave this
discussion until I read 0/4 at least.

Oleg.