From: "Paul E. McKenney" <paul...@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...@intel.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Alexey Kuznetsov <kuz...@ms2.inr.ac.ru>
Cc: James Morris <jmor...@namei.org>
Cc: Hideaki YOSHIFUJI <yoshf...@linux-ipv6.org>
Cc: Patrick McHardy <ka...@trash.net>
Cc: net...@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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