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Subject[PATCH 3.16 211/233] ipv6: only call ip6_route_dev_notify() once for NETDEV_UNREGISTER
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: WANG Cong <xiyou.wangcong@gmail.com>

commit 76da0704507bbc51875013f6557877ab308cfd0a upstream.

In commit 242d3a49a2a1 ("ipv6: reorder ip6_route_dev_notifier after ipv6_dev_notf")
I assumed NETDEV_REGISTER and NETDEV_UNREGISTER are paired,
unfortunately, as reported by jeffy, netdev_wait_allrefs()
could rebroadcast NETDEV_UNREGISTER event until all refs are
gone.

We have to add an additional check to avoid this corner case.
For netdev_wait_allrefs() dev->reg_state is NETREG_UNREGISTERED,
for dev_change_net_namespace(), dev->reg_state is
NETREG_REGISTERED. So check for dev->reg_state != NETREG_UNREGISTERED.

Fixes: 242d3a49a2a1 ("ipv6: reorder ip6_route_dev_notifier after ipv6_dev_notf")
Reported-by: jeffy <jeffy.chen@rock-chips.com>
Cc: David Ahern <dsahern@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv6/route.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2835,7 +2835,11 @@ static int ip6_route_dev_notify(struct n
net->ipv6.ip6_blk_hole_entry->dst.dev = dev;
net->ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_get(dev);
#endif
- } else if (event == NETDEV_UNREGISTER) {
+ } else if (event == NETDEV_UNREGISTER &&
+ dev->reg_state != NETREG_UNREGISTERED) {
+ /* NETDEV_UNREGISTER could be fired for multiple times by
+ * netdev_wait_allrefs(). Make sure we only call this once.
+ */
in6_dev_put(net->ipv6.ip6_null_entry->rt6i_idev);
#ifdef CONFIG_IPV6_MULTIPLE_TABLES
in6_dev_put(net->ipv6.ip6_prohibit_entry->rt6i_idev);
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