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    Subject[PATCH v2 tip/core/rcu 08/13] ipv6/ip6_gre: Apply rcu_access_pointer() to avoid sparse false positive
    Date
    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
    ip6gre_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 rcu_access_pointer() as suggested by 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/ipv6/ip6_gre.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
    index 6b26e9feafb9..a0b8f4056f05 100644
    --- a/net/ipv6/ip6_gre.c
    +++ b/net/ipv6/ip6_gre.c
    @@ -276,7 +276,7 @@ static void ip6gre_tunnel_unlink(struct ip6gre_net *ign, struct ip6_tnl *t)
    (iter = rtnl_dereference(*tp)) != NULL;
    tp = &iter->next) {
    if (t == iter) {
    - rcu_assign_pointer(*tp, t->next);
    + rcu_assign_pointer(*tp, rcu_access_pointer(t->next));
    break;
    }
    }
    --
    1.8.1.5


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