netdev - Re: [PATCH net] ipv4: add reference counting to metrics

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Date:   Fri, 26 May 2017 14:58:24 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     edumazet@...gle.com, andreyknvl@...gle.com, ja@....bg,
        xiyou.wangcong@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv4: add reference counting to metrics

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 25 May 2017 14:27:35 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Andrey Konovalov reported crashes in ipv4_mtu()
> 
> I could reproduce the issue with KASAN kernels, between
> 10.246.7.151 and 10.246.7.152 :
> 
> 1) 20 concurrent netperf -t TCP_RR -H 10.246.7.152 -l 1000 &
> 
> 2) At the same time run following loop :
> while :
> do
>  ip ro add 10.246.7.152 dev eth0 src 10.246.7.151 mtu 1500
>  ip ro del 10.246.7.152 dev eth0 src 10.246.7.151 mtu 1500
> done
> 
> 
> Cong Wang attempted to add back rt->fi in commit
> 82486aa6f1b9 ("ipv4: restore rt->fi for reference counting")
> but this proved to add some issues that were complex to solve.
> 
> Instead, I suggested to add a refcount to the metrics themselves,
> being a standalone object (in particular, no reference to other objects)
> 
> I tried to make this patch as small as possible to ease its backport,
> instead of being super clean. Note that we believe that only ipv4 dst
> need to take care of the metric refcount. But if this is wrong,
> this patch adds the basic infrastructure to extend this to other
> families.
> 
> Many thanks to Julian Anastasov for reviewing this patch, and Cong Wang
> for his efforts on this problem.
> 
> Fixes: 2860583fe840 ("ipv4: Kill rt->fi")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>

Applied, thanks everyone for following through on this bug fix.

And sorry for introducing the problem in the first place :)