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
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 ACCESS_ONCE() as suggested by Eric Dumazet and 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: Thomas Graf <tg...@suug.ch>
Cc: Gao feng <gaof...@cn.fujitsu.com>
Cc: Stephen Hemminger <shemmin...@vyatta.com>
Cc: linux-decnet-u...@lists.sourceforge.net
Cc: net...@vger.kernel.org
---
net/decnet/dn_route.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index fe32388ea24f..a6ef8b025035 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -344,8 +344,9 @@ static int dn_insert_route(struct dn_route *rt, unsigned
int hash, struct dn_rou
if (compare_keys(&rth->fld, &rt->fld)) {
/* Put it first */
*rthp = rth->dst.dn_next;
- rcu_assign_pointer(rth->dst.dn_next,
- dn_rt_hash_table[hash].chain);
+ /* Both --rcu and visible, so ACCESS_ONCE() is OK. */
+ ACCESS_ONCE(rth->dst.dn_next) =
+ dn_rt_hash_table[hash].chain;
rcu_assign_pointer(dn_rt_hash_table[hash].chain, rth);
dst_use(&rth->dst, now);
@@ -358,7 +359,8 @@ 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);
+ /* Both --rcu and visible, so ACCESS_ONCE() is OK. */
+ ACCESS_ONCE(rt->dst.dn_next) = 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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