ipv6: don't release rt->rt6i_pcpu memory during rt6_release()

After rwlock is replaced with rcu and spinlock, route lookup can happen
simultanously with route deletion.
This patch removes the call to free_percpu(rt->rt6i_pcpu) from
rt6_release() to avoid the race condition between rt6_release() and
rt6_get_pcpu_route(). And as free_percpu(rt->rt6i_pcpu) is already
called in ip6_dst_destroy() after the rcu grace period, it is safe to do
this change.
Signed-off-by: NWei Wang <weiwan@google.com>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -190,9 +190,6 @@ void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
 			*ppcpu_rt = NULL;
 		}
 	}
-
-	free_percpu(non_pcpu_rt->rt6i_pcpu);
-	non_pcpu_rt->rt6i_pcpu = NULL;
 }
 EXPORT_SYMBOL_GPL(rt6_free_pcpu);