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

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Date:   Mon, 03 Jun 2019 12:43:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jwi@...ux.ibm.com
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

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 Fix-up the various call sites to check whether the dst is obsolete, and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.