On Wed, 2013-10-09 at 14:29 -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
>
> The sparse checking for rcu_assign_pointer() was recently upgraded
> to reject non-__kernel address spaces. This also rejects __rcu,
> which is almost always the right thing to do. However, the use in
> ip6_tnl_unlink() is legitimate: It is assigning a pointer to an element
> from an RCU-protected list, and all elements of this list are already
> visible to caller.
>
> This commit therefore silences this false positive by laundering the
> pointer using rcu_access_pointer() as suggested by Josh Triplett.
>
> Reported-by: kbuild test robot <fengguang...@intel.com>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: "David S. Miller" <da...@davemloft.net>
> Cc: Alexey Kuznetsov <kuz...@ms2.inr.ac.ru>
> Cc: James Morris <jmor...@namei.org>
> Cc: Hideaki YOSHIFUJI <yoshf...@linux-ipv6.org>
> Cc: Patrick McHardy <ka...@trash.net>
> Cc: net...@vger.kernel.org
> ---
> net/ipv6/ip6_tunnel.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
> index 61355f7f4da5..ecc0166e1a9c 100644
> --- a/net/ipv6/ip6_tunnel.c
> +++ b/net/ipv6/ip6_tunnel.c
> @@ -245,7 +245,7 @@ ip6_tnl_unlink(struct ip6_tnl_net *ip6n, struct ip6_tnl
> *t)
> (iter = rtnl_dereference(*tp)) != NULL;
> tp = &iter->next) {
> if (t == iter) {
> - rcu_assign_pointer(*tp, t->next);
> + rcu_assign_pointer(*tp, rcu_access_pointer(t->next));
> break;
> }
> }
Then it seems a mere "*tp = t->next;" would be enough ?
We do not really need a barrier.
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