Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 04/14] decnet: Apply ACCESS_ONCE() to avoid sparse false positive | Date | Fri, 15 Nov 2013 16:40:07 -0800 |
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From: "Paul E. McKenney" <paulmck@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.wu@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Thomas Graf <tgraf@suug.ch> Cc: Gao feng <gaofeng@cn.fujitsu.com> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: linux-decnet-user@lists.sourceforge.net Cc: netdev@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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