[PATCH v3 tip/core/rcu 04/14] wireless: Apply ACCESS_ONCE() to avoid sparse false positive
From: Paul E. McKenney <hidden>
Date: 2013-10-11 23:18:22
Also in:
bridge, lkml
Subsystem:
802.11 (including cfg80211/nl80211), the rest · Maintainers:
Johannes Berg, Linus Torvalds
From: "Paul E. McKenney" <redacted> 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 <redacted> Signed-off-by: Paul E. McKenney <redacted> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: "David S. Miller" <davem@davemloft.net> 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