From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu, 14 May 2015 14:02:30 +0800

The commit c5adde9468b0714a051eac7f9666f23eb10b61f7 ("netlink:
eliminate nl_sk_hash_lock") added a lock_sock to netlink_insert
with no justifications whatsoever.

This patch kills it.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Actually, Herbert, I think this lock_sock() is needed.

Otherwise nothing protects nlk_sk(sk)->portid, upon which we
perform a non-atomic test-and-set operation here.

If you remove the lock_sock(), two parallel bind/inserts are
possible on the same socket, potentially resulting in socket
state corruption.