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Date: Wed, 2 Sep 2015 13:58:02 -0700 From: Martin KaFai Lau <kafai@...com> To: Eric Dumazet <eric.dumazet@...il.com> CC: netdev <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Kernel Team <kernel-team@...com> Subject: Re: [PATCH net 3/3] ipv6: Fix dst_entry refcnt bugs in ip6_tunnel On Tue, Sep 01, 2015 at 01:14:20PM -0700, Eric Dumazet wrote: > > 2. Use a spinlock to protect the dst_cache operations > > Well, a seqlock would be better : No need for an atomic operation in > fast path. > seqlock can ensure consistency between idst->dst and idst->cookie. However, IPv6 dst destruction is not protected by rcu. dst_free() is directly called, like in ip6_fib.c and a few other places. Hence, atomic_inc_not_zero() cannot be used here because the dst may have already been kmem_cache_free() when refcnt is 0. A spinlock is needed to stop the ip6_tnl_dst_set() side from removing the refcnt. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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