Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 09/14] mac80211: Apply ACCESS_ONCE() to avoid sparse false positive | Date | Fri, 15 Nov 2013 16:40:12 -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 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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