[PATCH tip/core/rcu 09/13] ipv6/sit: Apply rcu_access_pointer() to avoid sparse false positive

From: Paul E. McKenney
Date: Tue Sep 24 2013 - 21:38:08 EST

From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

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
ipip6_tunnel_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.wu@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: Patrick McHardy <kaber@xxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
net/ipv6/sit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 7ee5cb9..fcb050a 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -157,7 +157,7 @@ static void ipip6_tunnel_unlink(struct sit_net *sitn, struct ip_tunnel *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));

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