Re: Anomalies while handling p_nstopchild count

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Sat, 10 Oct 2015 13:49:52 +0000 (UTC)
   From: christos%astron.com@localhost (Christos Zoulas)

   In article <Pine.NEB.4.64.1510101636500.411%vps1.whooppee.com@localhost>,
   Paul Goyette  <paul%whooppee.com@localhost> wrote:
   >-=-=-=-=-=-
   >+
   >+		if (!mutex_tryenter(proc_lock)) {
   >+			mutex_exit(p->p_lock);
   >+			mutex_enter(proc_lock);
   >+			mutex_enter(p->p_lock);
   >+		}

   Can you find out where exit1() is called with the proc_lock held? Then
   you can call it with an additional flag and remove the tryenter call,
   and instead use the flag.

I don't think that's why he put that there -- it's just that the lock
order is proc_lock first, then p->p_lock for any p.  This is the
optimistic reverse-order locking fragment that the mutex(9) man page
suggests.