genetlink: fix netns vs. netlink table locking

Since my commits introducing netns awareness into
genetlink we can get this problem:

BUG: scheduling while atomic: modprobe/1178/0x00000002
2 locks held by modprobe/1178:
 #0:  (genl_mutex){+.+.+.}, at: [<ffffffff8135ee1a>] genl_register_mc_grou
 #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff8135eeb5>] genl_register_mc_g
Pid: 1178, comm: modprobe Not tainted 2.6.31-rc8-wl-34789-g95cb731-dirty #
Call Trace:
 [<ffffffff8103e285>] __schedule_bug+0x85/0x90
 [<ffffffff81403138>] schedule+0x108/0x588
 [<ffffffff8135b131>] netlink_table_grab+0xa1/0xf0
 [<ffffffff8135c3a7>] netlink_change_ngroups+0x47/0x100
 [<ffffffff8135ef0f>] genl_register_mc_group+0x12f/0x290

because I overlooked that netlink_table_grab() will
schedule, thinking it was just the rwlock. However,
in the contention case, that isn't actually true.

Fix this by letting the code grab the netlink table
lock first and then the RCU for netns protection.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 0fbecbbe8e9e..080f6ba9e73a 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -176,12 +176,16 @@ struct netlink_skb_parms
 #define NETLINK_CREDS(skb)      (&NETLINK_CB((skb)).creds)
 
 
+extern void netlink_table_grab(void);
+extern void netlink_table_ungrab(void);
+
 extern struct sock *netlink_kernel_create(struct net *net,
                                           int unit,unsigned int groups,
                                           void (*input)(struct sk_buff *skb),
                                           struct mutex *cb_mutex,
                                           struct module *module);
 extern void netlink_kernel_release(struct sock *sk);
+extern int __netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern void netlink_clear_multicast_users(struct sock *sk, unsigned int group);
 extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);