netdev - Re: [RFC PATCH] bnx2x: fix tx queue locking and memory barriers

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Message-ID: <20100225170308.6294aa1a@dhcp-lab-109.englab.brq.redhat.com>
Date:	Thu, 25 Feb 2010 17:03:08 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	"Vladislav Zolotarov" <vladz@...adcom.com>
Cc:	"David Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Eilon Greenstein" <eilong@...adcom.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>
Subject: Re: [RFC PATCH] bnx2x: fix tx queue locking and memory barriers

On Thu, 25 Feb 2010 07:49:48 -0800
"Vladislav Zolotarov" <vladz@...adcom.com> wrote:

> In bnx2x_start_xmit(): right after the "stop queue" there is an smp_mb(), which will bring the cpu0 cache and a fresh fp->tx_bd_cons value to cpu1 and the following if() will return true and the queue will be released from bnx2x_start_xmit() flow.

If I understand correctly what is written in Documentation/memory-barriers.txt
this smp_mb() need to have another "paired" smp_{w}mb() on cpu0 to make value
be updated on cpu1, which is missing.
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