From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net 3/3] ipv6: Fix dst_entry refcnt bugs in ip6_tunnel
Date: Wed, 02 Sep 2015 15:48:57 -0700
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Cc: netdev <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Kernel Team <kernel-team@fb.com>
To: Martin KaFai Lau <kafai@fb.com>
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On Wed, 2015-09-02 at 14:52 -0700, Martin KaFai Lau wrote:
> On Wed, Sep 02, 2015 at 02:30:45PM -0700, Eric Dumazet wrote:
> > Object cannot be freed until all cpus have exited their RCU sections.
> You meant the dst_destroy() here will wait for all cpus exited their RCU sections?
> 
> static inline void dst_free(struct dst_entry *dst)
> {
> 	if (dst->obsolete > 0)
> 		return;
> 	if (!atomic_read(&dst->__refcnt)) {
> 		dst = dst_destroy(dst);
> 		if (!dst)
> 			return;
> 	}
> 	__dst_free(dst);
> }

dst_free() is called after RCU grace period, in the case you are
interested in.

Look at dst_rcu_free() and rt_free()