Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 05/14] ipv4/ip_socketglue: Apply ACCESS_ONCE() to avoid sparse false positive | Date | Fri, 15 Nov 2013 16:40:08 -0800 |
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From: "Paul E. McKenney" <paulmck@linux.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 ip_ra_control() 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@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Cc: James Morris <jmorris@namei.org> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org> Cc: Patrick McHardy <kaber@trash.net> Cc: netdev@vger.kernel.org --- net/ipv4/ip_sockglue.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index d9c4f113d709..a0e7f176e9c8 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -269,7 +269,8 @@ int ip_ra_control(struct sock *sk, unsigned char on, } /* dont let ip_call_ra_chain() use sk again */ ra->sk = NULL; - rcu_assign_pointer(*rap, ra->next); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(*rap) = ra->next; spin_unlock_bh(&ip_ra_lock); if (ra->destructor) -- 1.8.1.5
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