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Date:   Mon, 25 Sep 2017 22:52:38 -0700
From:   Wei Wang <>
To:     Eric Dumazet <>
Cc:     Martin KaFai Lau <>,
        David Miller <>,
        Linux Kernel Network Developers <>
Subject: Re: [PATCH net] ipv6: remove incorrect WARN_ON() in fib6_del()

On Mon, Sep 25, 2017 at 7:23 PM, Eric Dumazet <> wrote:
> On Mon, Sep 25, 2017 at 7:07 PM, Martin KaFai Lau <> wrote:
>> I am probably still missing something.
>> Considering the del operation should be under the writer lock,
>> if rt->rt6i_node should be NULL (for rt that has already been
>> removed from fib6), why this WARN_ON() is triggered?
>> An example may help.
> Look at the stack trace, you'll find the answers...
> ip6_link_failure() -> ip6_del_rt()
> Note that rt might have been deleted from the _tree_ already.

Had a brief talk with Martin.
He has a valid point.
The current WARN_ON() code is as follows:
#if RT6_DEBUG >= 2
       if (rt->dst.obsolete > 0) {
               return -ENOENT;

The WARN_ON() only triggers when fn is not NULL. (I missed it before.)
In theory, fib6_del() calls fib6_del_route() which should set
rt->rt6i_node to NULL and rt->dst.obsolete to DST_OBSOLETE_DEAD within
the same write_lock session.
If those 2 values are inconsistent, it indicates something is wrong.
Will need more time to root cause the issue.

Please ignore this patch. Sorry about the confusion.

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