Re: [memnic PATCH 1/5] pmd: fix race condition

[Olivier MATZ <olivier.matz-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>]

Hi Hiroshi-san,

Please see my comments below.

On 03/11/2014 06:37 AM, Hiroshi Shimamoto wrote:
> From: Hiroshi Shimamoto <h-shimamoto-ehU+Cx/zZe18UrSeD/g0lQ@public.gmane.org>
> 
> There is a race condition, on transmit to vSwitch.

I think we should not talk specifically about vSwitch, as
another implementation of host memnic is possible. Maybe using
the term "host" is more appropriate?

> +		if (idx != ACCESS_ONCE(adapter->down_idx)) {
> +			/*
> +			 * vSwitch freed this and got false positive,
> +			 * need to recover the status and retry.
> +			 */
> +			p->status = MEMNIC_PKT_ST_FREE;
> +			goto retry;
> +		}
> +

The patch indeed looks to improve reliability, even if it's
difficult to me to be sure that there is no other race condition.
Again, I would replace "vSwitch" by "host".

By the way, I guess the Linux code in linux/memnic_net.c should be
modified in the same way.

Regards,
Olivier