netdev - Re: [PATCH net-next 1/4] ipv6: Calculate hash thresholds for IPv6 nexthops

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Date:   Wed, 2 May 2018 09:43:50 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Ahern <dsahern@...il.com>,
        Ido Schimmel <idosch@...lanox.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, roopa@...ulusnetworks.com,
        nikolay@...ulusnetworks.com, pch@...bogen.com, jkbs@...hat.com,
        yoshfuji@...ux-ipv6.org, mlxsw@...lanox.com
Subject: Re: [PATCH net-next 1/4] ipv6: Calculate hash thresholds for IPv6
 nexthops



On 01/09/2018 07:43 PM, David Ahern wrote:
> On 1/9/18 7:40 AM, Ido Schimmel wrote:
>> Before we convert IPv6 to use hash-threshold instead of modulo-N, we
>> first need each nexthop to store its region boundary in the hash
>> function's output space.
>>
>> The boundary is calculated by dividing the output space equally between
>> the different active nexthops. That is, nexthops that are not dead or
>> linkdown.
>>
>> The boundaries are rebalanced whenever a nexthop is added or removed to
>> a multipath route and whenever a nexthop becomes active or inactive.
>>
>> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
>> ---
>>  include/net/ip6_fib.h   |  1 +
>>  include/net/ip6_route.h |  7 ++++
>>  net/ipv6/ip6_fib.c      |  8 ++---
>>  net/ipv6/route.c        | 96 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  4 files changed, 106 insertions(+), 6 deletions(-)
>>
> 
> LGTM.
> Acked-by: David Ahern <dsahern@...il.com>
> 

For some reason I have a divide by zero error booting my hosts with latest net tree.

What guarantee do we have that total is not zero when rt6_upper_bound_set() is called ?



[    8.498639] divide error: 0000 [#1] SMP PTI
[    8.503178] gsmi: Log Shutdown Reason 0x03
[    8.507270] Modules linked in: bnx2x mdio
[    8.511276] CPU: 17 PID: 116 Comm: kworker/17:0 Not tainted 4.17.0-smp-DEV #110
[    8.518571] Hardware name: Intel RML,PCH/Ibis_QC_18, BIOS 2.40.0 06/22/2016
[    8.525526] Workqueue: ipv6_addrconf addrconf_dad_work
[    8.530662] RIP: 0010:rt6_multipath_rebalance.part.82+0x1cb/0x1f0
[    8.536752] RSP: 0018:ffffba72867cbbf8 EFLAGS: 00010246
[    8.541966] RAX: 0000000000000000 RBX: 0000000000000025 RCX: ffff9d555ab73180
[    8.549090] RDX: 0000000000000000 RSI: ffff9d4d5a34b1c0 RDI: 0000000000000000
[    8.556212] RBP: ffffba72867cbc00 R08: 0000000000000000 R09: 0000000000000000
[    8.563336] R10: 0000000000000000 R11: 0000000000000000 R12: ffff9d5559f95680
[    8.570457] R13: ffff9d4d5a34b1c0 R14: ffff9d555ab73180 R15: 0000000000000000
[    8.577579] FS:  0000000000000000(0000) GS:ffff9d4d5fc40000(0000) knlGS:0000000000000000
[    8.585654] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    8.591391] CR2: 00007fffe47ff000 CR3: 0000000c39c0a001 CR4: 00000000000606e0
[    8.598515] Call Trace:
[    8.600961]  ? rt6_multipath_rebalance+0x21/0x30
[    8.605579]  fib6_add+0x75f/0xf70
[    8.608899]  ? __wake_up+0x13/0x20
[    8.612303]  ? netlink_broadcast_filtered+0x14c/0x3c0
[    8.617355]  __ip6_ins_rt+0x4c/0x70
[    8.620847]  ip6_ins_rt+0x6e/0xa0
[    8.624157]  __ipv6_ifa_notify+0x226/0x2e0
[    8.628249]  ipv6_ifa_notify+0x2a/0x40
[    8.631999]  addrconf_dad_completed+0x59/0x360
[    8.636438]  addrconf_dad_work+0x11c/0x400
[    8.640536]  ? addrconf_dad_work+0x11c/0x400
[    8.644810]  process_one_work+0x184/0x370
[    8.648820]  ? process_one_work+0x184/0x370
[    8.652996]  worker_thread+0x35/0x3a0
[    8.656654]  kthread+0x121/0x140
[    8.659887]  ? process_one_work+0x370/0x370
[    8.664073]  ? kthread_create_worker_on_cpu+0x70/0x70
[    8.669118]  ret_from_fork+0x35/0x40
[    8.672693] Code: c3 8b b9 38 01 00 00 eb aa 48 63 81 38 01 00 00 89 fa 41 89 f8 c1 ea 1f 01 fa d1 fa 48 63 d2 49 89 c2 48 c1 e0 1f 48 01 d0 31 d2 <49> f7 f0 83 e8 01 48 39 ce 89 81 b4 00 00 00 0f 85 e2 fe ff ff 
[    8.691533] RIP: rt6_multipath_rebalance.part.82+0x1cb/0x1f0 RSP: ffffba72867cbbf8
[    8.699135] ---[ end trace 9ae26819121cdc3a ]---
[    8.703760] Kernel panic - not syncing: Fatal exception in interrupt
[    8.710169] Kernel Offset: 0x3d200000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[    8.721256] gsmi: Log Shutdown Reason 0x02
[    8.725357] Rebooting in 10 seconds..