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Message-Id: <20190308.105122.656526755979170615.davem@davemloft.net>
To:     lucien.xin@gmail.com
Cc:     netdev@vger.kernel.org, dsahern@gmail.com, jmaxwell37@gmail.com,
        jmaxwell@redhat.com
Subject: Re: [PATCH net] route: set the deleted fnhe fnhe_daddr to 0 in
 ip_del_fnhe to fix a race
From:   David Miller <davem@davemloft.net>
In-Reply-To: <42a31507d9b1d4874bb9a8570bd9f17225aaa553.1552027854.git.lucien.xin@gmail.com>
References: <42a31507d9b1d4874bb9a8570bd9f17225aaa553.1552027854.git.lucien.xin@gmail.com>
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From: Xin Long <lucien.xin@gmail.com>
Date: Fri,  8 Mar 2019 14:50:54 +0800

> The race occurs in __mkroute_output() when 2 threads lookup a dst:
> 
>   CPU A                 CPU B
>   find_exception()
>                         find_exception() [fnhe expires]
>                         ip_del_fnhe() [fnhe is deleted]
>   rt_bind_exception()
> 
> In rt_bind_exception() it will bind a deleted fnhe with the new dst, and
> this dst will get no chance to be freed. It causes a dev defcnt leak and
> consecutive dmesg warnings:
> 
>   unregister_netdevice: waiting for ethX to become free. Usage count = 1
> 
> Especially thinks Jon to identify the issue.

I did "s/thinks/thanks/" here.

> This patch fixes it by setting fnhe_daddr to 0 in ip_del_fnhe() to stop
> binding the deleted fnhe with a new dst when checking fnhe's fnhe_daddr
> and daddr in rt_bind_exception().
> 
> It works as both ip_del_fnhe() and rt_bind_exception() are protected by
> fnhe_lock and the fhne is freed by kfree_rcu().
> 
> Fixes: deed49df7390 ("route: check and remove route cache when we get route")
> Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queues up for -stable, thank you.