netdev - Re: [PATCH net] ipv4: Avoid caching dsts when lookup skipped nh oif check

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Date:   Thu, 20 Apr 2017 16:35:16 +0100
From:   Robert Shearman <rshearma@...cade.com>
To:     David Ahern <dsa@...ulusnetworks.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>
Subject: Re: [PATCH net] ipv4: Avoid caching dsts when lookup skipped nh oif
 check

On 20/04/17 16:16, David Ahern wrote:
> On 4/20/17 9:05 AM, Robert Shearman wrote:
>> The key thing I think is the ip rules:
>>
>> $ ip rule
>> 0:    from all lookup local
>> 1000:    from all lookup [l3mdev-table]
>> 32766:    from all lookup main
>> 32767:    from all lookup default
>>
>> Maybe you have the local rule moved down at startup?
>
> yes that would be a problem. With this test the 127.0.0.1 lookup is
> matching on the wrong table:
>
> perf probe fib_table_lookup%return ret=%ax
> perf record -e fib:*,probe:* -a -- ping -c1 -w1 -I red 127.0.0.1
> ...
> perf script
>
...
> Table 255 is the wrong table. That is the ultimate problem here.
>

The table used for the lookup could be retrieved from the oif, but the 
check I introduced would still be required to cope with the unusual, but 
not disallowed, case of two VRF master devices referring to the same table.

Thanks,
Rob