netdev - Re: [PATCH net 2/4] s390/qeth: don't use obsolete dst entry

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Message-Id: <06972ee2-43ac-045f-8d7e-568752908ecd@linux.ibm.com>
Date:   Tue, 4 Jun 2019 10:03:59 +0200
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        heiko.carstens@...ibm.com, raspl@...ux.ibm.com,
        ubraun@...ux.ibm.com
Subject: Re: [PATCH net 2/4] s390/qeth: don't use obsolete dst entry

On 03.06.19 21:43, David Miller wrote:
> From: Julian Wiedmann <jwi@...ux.ibm.com>
> Date: Mon,  3 Jun 2019 17:04:44 +0200
> 
>> While qeth_l3 uses netif_keep_dst() to hold onto the dst, a skb's dst
>> may still have been obsoleted (via dst_dev_put()) by the time that we
>> end up using it. The dst then points to the loopback interface, which
>> means the neighbour lookup in qeth_l3_get_cast_type() determines a bogus
>> cast type of RTN_BROADCAST.
>> For IQD interfaces this causes us to place such skbs on the wrong
>> HW queue, resulting in TX errors.
>>
>> Fix-up the various call sites to check whether the dst is obsolete, and
>> fall back accordingly.
>>
>> Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
> 
> Please use "dst_check()".
> 
> Some routes have DST_OBSOLETE_FORCE_CHK set on them from the very beginning
> so that uses of the route are forced through the dst->ops->check() method.
> 
> Simply use dst_check() and then you can just retain the 'rt == NULL' logic
> as-is.
> 
> Thanks.
> 
Alright - I was hesitant to go down that path in the context of a driver,
but looks like rt6_get_cookie() should do the trick. v2 coming up... thanks.