From patchwork Fri Oct 11 23:17:27 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. 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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 v3 tip/core/rcu 10/14] mac80211: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 11 Oct 2013 16:17:27 -0700 Message-Id: <1381533451-29018-10-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1381533451-29018-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131011231659.GA28062@linux.vnet.ibm.com> <1381533451-29018-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13101123-1542-0000-0000-000002374736 Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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; }