netdev - Re: [PATCH] ixgbe: Check for skb->queue

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Date:   Wed, 29 Mar 2017 18:47:34 -0700
From:   tndave <tushar.n.dave@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     jeffrey.t.kirsher@...el.com, intel-wired-lan@...ts.osuosl.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] ixgbe: Check for skb->queue_mapping



On 03/29/2017 05:29 PM, Eric Dumazet wrote:
> On Wed, 2017-03-29 at 16:55 -0700, Tushar Dave wrote:
>> There are events seen where skb->queue_mapping value is greater than
>> adapter->num_tx_queue. In such cases, adapter->tx_ring becomes invalid
>> (null) and xmit results in kernel panic.
>>
>> One such event is running netconsole and enabling VF on the same device.
>> Or running netconsole and changing number of tx queues via ethtool on
>> same device.
>>
>> This patch adds check for skb->queue_mapping and uses simple arithmetic
>> to select available tx queue from driver.
>
> We are not going to fix all multi queue drivers, for something that
> seems to be a generic issue higher in the stack.
I have fixed it in ixgbe,i40e drivers because I see Intel igb driver
does similar thing. But I agree that the core issue lies up in the stack.

For the information, I found that this issue only affecting skbs that
are coming from direct xmit path (netdev_start_xmit) that netconsole,
pktgen , af_packet etc,. uses. skbs coming from qdisc already have this
fixed in stack. (http://lists.openwall.net/netdev/2010/07/01/58)

Thanks.

-Tushar


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