Re: Anomalies while handling p_nstopchild count

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

On Mon, 12 Oct 2015, Taylor R Campbell wrote:

>   In kern/kern_exit.c at (original) line 231, there's a call to
>   membar_producer(), presumably to ensure that p->p_waited is globally
>   visible before updating p_.p_stat (which might cause someone to look
>   at p->p_waited).
>
>   Now that I'm planning to protect this whole area using proc_lock, I
>   question whether or not the potentially expensive call to
>   membar_producer() is still needed?
>
> The membar_producer is certainly longer be needed.  It is not clear to
> me why it was needed in the first place, nor is the original commit
> message (kern_exit.c 1.158.2.6, `Checkpoint work in progress' on the
> newlock2 branch) illuminating.  I see no matching membar_consumer,
> even in the CVS logs.
>
> My guess is that the membar_producer was an aborted attempt to avoid
> locks or atomics for a certain part of the signal/wait protocol.

Thanks for the confirmation.  I will remove it when I commit the final
patch.


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