netdev - Re: [PATCH net] ipv6: remove incorrect WARN_ON() in fib6

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Date:   Mon, 25 Sep 2017 18:16:05 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] ipv6: remove incorrect WARN_ON() in fib6_del()

On Mon, Sep 25, 2017 at 5:56 PM, Martin KaFai Lau <kafai@...com> wrote:
> On Mon, Sep 25, 2017 at 05:35:22PM +0000, Wei Wang wrote:
>> From: Wei Wang <weiwan@...gle.com>
>>
>> fib6_del() generates WARN_ON() when rt->dst.obsolete > 0. This does not
>> make sense because it is possible that the route passed in is already
>> deleted by some other thread and rt->dst.obsolete is set to
>> DST_OBSOLETE_DEAD.
>> So this commit deletes this WARN_ON() and also remove the
>> "#ifdef RT6_DEBUG >= 2" condition so that if the route is already
>> obsolete, we return right at the beginning of fib6_del().
>>
>>
>> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
>> index e5308d7cbd75..693bcd7ef6d2 100644
>> --- a/net/ipv6/ip6_fib.c
>> +++ b/net/ipv6/ip6_fib.c
>> @@ -1592,13 +1592,7 @@ int fib6_del(struct rt6_info *rt, struct nl_info *info)
>>       struct net *net = info->nl_net;
>>       struct rt6_info **rtp;
>>
>> -#if RT6_DEBUG >= 2
>> -     if (rt->dst.obsolete > 0) {
>> -             WARN_ON(fn);
> fn should have already been set to NULL if it is removed
> from the fib6 tree?
>

That is true. rt->rt6i_node (fn) should already be marked as NULL.
That means the check on rt->dst.obsolete is redundant.
I will remove it in v2.
Thanks Martin.


>> -             return -ENOENT;
>> -     }
>> -#endif
>> -     if (!fn || rt == net->ipv6.ip6_null_entry)
>> +     if (!fn || rt->dst.obsolete > 0 || rt == net->ipv6.ip6_null_entry)
>>               return -ENOENT;
>>
>>       WARN_ON(!(fn->fn_flags & RTN_RTINFO));
>> --
>> 2.14.1.821.g8fa685d3b7-goog
>>