From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from e31.co.us.ibm.com ([32.97.110.149]:53639 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754856Ab3KPAk2 (ORCPT ); Fri, 15 Nov 2013 19:40:28 -0500 Received: from /spool/local by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 15 Nov 2013 17:40:28 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "Paul E. McKenney" , "John W. Linville" , Johannes Berg , "David S. Miller" , linux-wireless@vger.kernel.org, netdev@vger.kernel.org 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 Message-Id: <1384562417-817-9-git-send-email-paulmck@linux.vnet.ibm.com> (sfid-20131116_014458_336498_237A5286) In-Reply-To: <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131116003946.GA316@linux.vnet.ibm.com> <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: From: "Paul E. McKenney" 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 Signed-off-by: Paul E. McKenney Cc: "John W. Linville" Cc: Johannes Berg Cc: "David S. Miller" 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