Re: Anomalies while handling p_nstopchild count

[Paul Goyette <paul%vps1.whooppee.com@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.

Correct.

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