* [PATCH tip/core/rcu 09/14] mac80211: Apply ACCESS_ONCE() to avoid sparse false positive
[not found] ` <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com>
@ 2013-11-16 0:40 ` Paul E. McKenney
0 siblings, 0 replies; only message in thread
From: Paul E. McKenney @ 2013-11-16 0:40 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, dhowells, edumazet, darren, fweisbec, sbw,
Paul E. McKenney, John W. Linville, Johannes Berg,
David S. Miller, linux-wireless, netdev
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 uses in
sta_info_hash_del() are legitimate: They are 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: "John W. Linville" <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
---
net/mac80211/sta_info.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index aeb967a0aeed..494f03c0831f 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -74,8 +74,8 @@ static int sta_info_hash_del(struct ieee80211_local *local,
if (!s)
return -ENOENT;
if (s == sta) {
- rcu_assign_pointer(local->sta_hash[STA_HASH(sta->sta.addr)],
- s->hnext);
+ /* Both --rcu and visible, so ACCESS_ONCE() is OK. */
+ ACCESS_ONCE(local->sta_hash[STA_HASH(sta->sta.addr)]) = s->hnext;
return 0;
}
@@ -84,7 +84,8 @@ static int sta_info_hash_del(struct ieee80211_local *local,
s = rcu_dereference_protected(s->hnext,
lockdep_is_held(&local->sta_mtx));
if (rcu_access_pointer(s->hnext)) {
- rcu_assign_pointer(s->hnext, sta->hnext);
+ /* Both --rcu and visible, so ACCESS_ONCE() is OK. */
+ ACCESS_ONCE(s->hnext) = sta->hnext;
return 0;
}
--
1.8.1.5
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