Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754939Ab3JKXSW (ORCPT ); Fri, 11 Oct 2013 19:18:22 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:59088 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754530Ab3JKXRp (ORCPT ); Fri, 11 Oct 2013 19:17:45 -0400 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" , Stephen Hemminger , "David S. Miller" , bridge@lists.linux-foundation.org, netdev@vger.kernel.org Subject: [PATCH v3 tip/core/rcu 04/14] wireless: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 11 Oct 2013 16:17:21 -0700 Message-Id: <1381533451-29018-4-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: 13101123-9332-0000-0000-000001BD30DF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4037 Lines: 106 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 cfg80211_combine_bsses() and cfg80211_bss_update() 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 these false positives by laundering the pointers using ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett. Reported-by: kbuild test robot Signed-off-by: Paul E. McKenney Cc: Stephen Hemminger Cc: "David S. Miller" Cc: bridge@lists.linux-foundation.org Cc: netdev@vger.kernel.org --- net/wireless/scan.c | 32 ++++++++++++++++++-------------- 1 file changed, 18 insertions(+), 14 deletions(-) diff --git a/net/wireless/scan.c b/net/wireless/scan.c index eeb71480f1af..ac3a47abf195 100644 --- a/net/wireless/scan.c +++ b/net/wireless/scan.c @@ -670,8 +670,8 @@ static bool cfg80211_combine_bsses(struct cfg80211_registered_device *dev, list_add(&bss->hidden_list, &new->hidden_list); bss->pub.hidden_beacon_bss = &new->pub; new->refcount += bss->refcount; - rcu_assign_pointer(bss->pub.beacon_ies, - new->pub.beacon_ies); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(bss->pub.beacon_ies) = new->pub.beacon_ies; } return true; @@ -705,11 +705,12 @@ cfg80211_bss_update(struct cfg80211_registered_device *dev, old = rcu_access_pointer(found->pub.proberesp_ies); - rcu_assign_pointer(found->pub.proberesp_ies, - tmp->pub.proberesp_ies); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(found->pub.proberesp_ies) = + tmp->pub.proberesp_ies; /* Override possible earlier Beacon frame IEs */ - rcu_assign_pointer(found->pub.ies, - tmp->pub.proberesp_ies); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(found->pub.ies) = tmp->pub.proberesp_ies; if (old) kfree_rcu((struct cfg80211_bss_ies *)old, rcu_head); @@ -739,13 +740,14 @@ cfg80211_bss_update(struct cfg80211_registered_device *dev, old = rcu_access_pointer(found->pub.beacon_ies); - rcu_assign_pointer(found->pub.beacon_ies, - tmp->pub.beacon_ies); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(found->pub.beacon_ies) = tmp->pub.beacon_ies; /* Override IEs if they were from a beacon before */ if (old == rcu_access_pointer(found->pub.ies)) - rcu_assign_pointer(found->pub.ies, - tmp->pub.beacon_ies); + /* Both --rcu & visible, ACCESS_ONCE() is OK. */ + ACCESS_ONCE(found->pub.ies) = + tmp->pub.beacon_ies; /* Assign beacon IEs to all sub entries */ list_for_each_entry(bss, &found->hidden_list, @@ -755,8 +757,9 @@ cfg80211_bss_update(struct cfg80211_registered_device *dev, ies = rcu_access_pointer(bss->pub.beacon_ies); WARN_ON(ies != old); - rcu_assign_pointer(bss->pub.beacon_ies, - tmp->pub.beacon_ies); + /* Both --rcu & visible, ACCESS_ONCE() is OK. */ + ACCESS_ONCE(bss->pub.beacon_ies) = + tmp->pub.beacon_ies; } if (old) @@ -803,8 +806,9 @@ cfg80211_bss_update(struct cfg80211_registered_device *dev, list_add(&new->hidden_list, &hidden->hidden_list); hidden->refcount++; - rcu_assign_pointer(new->pub.beacon_ies, - hidden->pub.beacon_ies); + /* Both --rcu & visible, ACCESS_ONCE() is OK. */ + ACCESS_ONCE(new->pub.beacon_ies) = + hidden->pub.beacon_ies; } } else { /* -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/