netdev - Re: [PATCH net] ipv6: fix a dst leak when removing its exception

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Date:   Thu, 15 Nov 2018 10:17:16 -0800
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>
Subject: Re: [PATCH net] ipv6: fix a dst leak when removing its exception

On 11/14/18 11:23 PM, Xin Long wrote:
> On Thu, Nov 15, 2018 at 3:33 PM David Ahern <dsa@...ulusnetworks.com> wrote:
>>
>> On 11/14/18 11:03 AM, David Ahern wrote:
>>> On 11/13/18 8:48 AM, Xin Long wrote:
>>>> These is no need to hold dst before calling rt6_remove_exception_rt().
>>>> The call to dst_hold_safe() in ip6_link_failure() was for ip6_del_rt(),
>>>> which has been removed in Commit 93531c674315 ("net/ipv6: separate
>>>> handling of FIB entries from dst based routes"). Otherwise, it will
>>>> cause a dst leak.
>>>>
>>>> This patch is to simply remove the dst_hold_safe() call before calling
>>>> rt6_remove_exception_rt() and also do the same in ip6_del_cached_rt().
>>>> It's safe, because the removal of the exception that holds its dst's
>>>> refcnt is protected by rt6_exception_lock.
>>>>
>>>> Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
>>>> Fixes: 23fb93a4d3f1 ("net/ipv6: Cleanup exception and cache route handling")
>>>> Reported-by: Li Shuang <shuali@...hat.com>
>>>> Signed-off-by: Xin Long <lucien.xin@...il.com>
>>>> ---
>>>>  net/ipv6/route.c | 7 +++----
>>>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>>
>>> was this problem actually hit or is this patch based on a code analysis?
>>>
>>
>> I ask because I have not been able to reproduce the leak using existing
>> tests (e.g., pmtu) that I know create exceptions.
>>
>> If this problem was hit, it would be good to get a test case for it.
> The attachment is the ip6_dst.sh with IPVS.
> 
> # sh ip6_dst.sh
> 
> But this one triggers the kernel warnings caused by 2 places:
>    unregister_netdevice: waiting for br0 to become free. Usage count = 3
> 
> 1. one is IPVS, I just posted the fix:
> https://patchwork.ozlabs.org/patch/998123/  [1]
> 2. the other one is IPv6,
> ip6_link_failure() will be hit.
> 
> So to make this reproduce clearly, you may want to apply
> patch [1] firstly.
> 

Thanks for the script. It does not replicate the problem using net-next
tree as of

commit 6d5db6c37929cb0a84e64ba0590a74593e5ce3b8
Merge: 15cef30974c5 bd3b5d462add
Author: David S. Miller <davem@...emloft.net>
Date:   Wed Nov 14 08:51:28 2018 -0800

    Merge branch 'nfp-abm-track-all-Qdiscs'


I would be really surprised if the fib6_info change introduced a need to
change the dst hold's for exception routes. I am not seeing the
connection, so I really want to see it reproduced.

Thanks