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

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Message-ID: <7204751a-70f9-5803-d5af-06b62530b762@cumulusnetworks.com>
Date:   Thu, 20 Apr 2017 09:16:56 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Robert Shearman <rshearma@...cade.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv4: Avoid caching dsts when lookup skipped nh oif
 check

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

            ping  2803 [000] 70559.086446: fib:fib_table_lookup: table
255 oif 31 iif 1 src 0.0.0.0 dst 127.0.0.1 tos 0 scope 0 flags 4
            ping  2803 [000] 70559.086451: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086453: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0
            ping  2803 [000] 70559.086458: fib:fib_table_lookup: table
255 oif 31 iif 1 src 127.0.0.1 dst 127.0.0.1 tos 0 scope 0 flags 4
            ping  2803 [000] 70559.086459: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086460: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0
            ping  2803 [000] 70559.086752: fib:fib_table_lookup: table
255 oif 31 iif 1 src 0.0.0.0 dst 127.0.0.1 tos 0 scope 0 flags 4
            ping  2803 [000] 70559.086754: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086755: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0
            ping  2803 [000] 70559.086768: fib:fib_table_lookup: table
255 oif 31 iif 1 src 127.0.0.1 dst 127.0.0.1 tos 0 scope 0 flags 5
            ping  2803 [000] 70559.086769: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086770: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0
            ping  2803 [000] 70559.086781: fib:fib_table_lookup: table
255 oif 31 iif 1 src 127.0.0.1 dst 127.0.0.1 tos 0 scope 0 flags 4
            ping  2803 [000] 70559.086782: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086782: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0
            ping  2803 [000] 70559.086787: fib:fib_table_lookup: table
255 oif 31 iif 1 src 127.0.0.1 dst 127.0.0.1 tos 0 scope 0 flags 5
            ping  2803 [000] 70559.086788: fib:fib_table_lookup_nh:
nexthop dev lo oif 1 src 127.0.0.1
            ping  2803 [000] 70559.086789: probe:fib_table_lookup:
(ffffffff8146aaaa <- ffffffff81470734) ret=0x0

Table 255 is the wrong table. That is the ultimate problem here.