[PATCH tip/core/rcu 05/13] decnet: Apply rcu_access_pointer() to avoid sparse false positive

From: Paul E. McKenney
Date: Tue Sep 24 2013 - 21:38:48 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
dn_insert_route() 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: Thomas Graf <tgraf@xxxxxxx>
Cc: Gao feng <gaofeng@xxxxxxxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: linux-decnet-user@xxxxxxxxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
---
net/decnet/dn_route.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index fe32388..3b1357b 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -345,7 +345,7 @@ static int dn_insert_route(struct dn_route *rt, unsigned int hash, struct dn_rou
/* Put it first */
*rthp = rth->dst.dn_next;
rcu_assign_pointer(rth->dst.dn_next,
- dn_rt_hash_table[hash].chain);
+ rcu_access_pointer(dn_rt_hash_table[hash].chain));
rcu_assign_pointer(dn_rt_hash_table[hash].chain, rth);

dst_use(&rth->dst, now);
@@ -358,7 +358,8 @@ static int dn_insert_route(struct dn_route *rt, unsigned int hash, struct dn_rou
rthp = &rth->dst.dn_next;
}

- rcu_assign_pointer(rt->dst.dn_next, dn_rt_hash_table[hash].chain);
+ rcu_assign_pointer(rt->dst.dn_next,
+ rcu_access_pointer(dn_rt_hash_table[hash].chain));
rcu_assign_pointer(dn_rt_hash_table[hash].chain, rt);

dst_use(&rt->dst, now);
--
1.8.1.5

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