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Date: Fri, 11 Oct 2013 16:17:26 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, darren@...art.com, fweisbec@...il.com, sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, "David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, James Morris <jmorris@...ei.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org Subject: [PATCH v3 tip/core/rcu 09/14] ipv6/sit: Apply ACCESS_ONCE() to avoid sparse false positive From: "Paul E. McKenney" <paulmck@...ux.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 use in ipip6_tunnel_unlink() is legitimate: It is 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@...el.com> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Cc: "David S. Miller" <davem@...emloft.net> Cc: Alexey Kuznetsov <kuznet@....inr.ac.ru> Cc: James Morris <jmorris@...ei.org> Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org> Cc: Patrick McHardy <kaber@...sh.net> Cc: netdev@...r.kernel.org --- net/ipv6/sit.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c index 7ee5cb96db34..9b976a4b463d 100644 --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -157,7 +157,8 @@ static void ipip6_tunnel_unlink(struct sit_net *sitn, struct ip_tunnel *t) (iter = rtnl_dereference(*tp)) != NULL; tp = &iter->next) { if (t == iter) { - rcu_assign_pointer(*tp, t->next); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(*tp) = t->next; break; } } -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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