netdev - Re: [PATCH] bnx2x: Prevent load reordering in tx completion processing

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Message-Id: <20190718.163042.844837284595324517.davem@davemloft.net>
Date:   Thu, 18 Jul 2019 16:30:42 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     brking@...ux.vnet.ibm.com
Cc:     GR-everest-linux-l2@...vell.com, skalluru@...vell.com,
        aelior@...vell.com, netdev@...r.kernel.org
Subject: Re: [PATCH] bnx2x: Prevent load reordering in tx completion
 processing

From: Brian King <brking@...ux.vnet.ibm.com>
Date: Mon, 15 Jul 2019 16:41:50 -0500

> This patch fixes an issue seen on Power systems with bnx2x which results
> in the skb is NULL WARN_ON in bnx2x_free_tx_pkt firing due to the skb
> pointer getting loaded in bnx2x_free_tx_pkt prior to the hw_cons
> load in bnx2x_tx_int. Adding a read memory barrier resolves the issue.
> 
> Signed-off-by: Brian King <brking@...ux.vnet.ibm.com>

I agree with Brian's explanation of how the reordering can happen, and why
the crash doesn't show up in the prefetch() call.

I'll give the Marvell folks one more day to give a proper ACK.

Thanks.