Re: [PATCH RFC 1/2] Add polling support to pidfd

[Oleg Nesterov]

On 04/19, Christian Brauner wrote:
>
> > Just for the exit notification purposes, the states are:
> > if process has exit_state == 0, block.
> > if process is zombie/dead but not reaped, then return POLLIN
> > if process is reaped, then return POLLIN | POLLHUP
>
> Oleg was explicitly against EXIT_ZOMBIE/DEAD thing, no? He said so in a
> prior mail. Has this been addressed?

Yes, please don't use EXIT_XXX codes, nobody should ever use them except the
core kernel exit/wait paths. For example, EXIT_DEAD means that the task auto-
reaps or its parent had to temporary drop tasklist.

Just check ->exit_state != 0 && thread_group_empty(). Note that we need
thread_group_empty() only for the case when the task is traced, in this case
we have an extra notification for debugger which can confuse pidfd_poll().

And of course, everything will differ if/when we will need to monitor the
sub-threads.

And btw I don't think it needs tasklist_lock, but lets discuss this when we
have a new version based on pidfd.

Oleg.