netdev - Re: Repeatable inet6_dump_fib crash in stock 4.12.0-rc4+

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Date:   Tue, 13 Jun 2017 14:42:50 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Ben Greear <greearb@...delatech.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Ahern <dsahern@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Repeatable inet6_dump_fib crash in stock 4.12.0-rc4+

On Tue, Jun 13, 2017 at 1:16 PM, Ben Greear <greearb@...delatech.com> wrote:
> On 06/09/2017 02:25 PM, Eric Dumazet wrote:
>>
>> On Fri, 2017-06-09 at 07:27 -0600, David Ahern wrote:
>>>
>>> On 6/8/17 11:55 PM, Cong Wang wrote:
>>>> Apparently fn->parent is NULL here for some reason, but
>>>> I don't know if that is expected or not. If a simple NULL check
>>>> is not enough here, we have to trace why it is NULL.
>>>
>>>
>>> From my understanding, parent should not be null hence the attempts to
>>> fix access to table nodes under a lock. ie., figuring out why it is null
>>> here.
>
>
> If someone has more suggestions, I'll be happy to test.

Can you enable RT6_TRACE() by changing RT6_DEBUG
from 2 to 3? We may collect some useful log with it.

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index d4bf2c6..1941595 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -37,7 +37,7 @@
 #include <net/ip6_fib.h>
 #include <net/ip6_route.h>

-#define RT6_DEBUG 2
+#define RT6_DEBUG 3

 #if RT6_DEBUG >= 3
 #define RT6_TRACE(x...) pr_debug(x)