First of all, this is my first attempt at locks, so I'd like early review.

Secondly, scripts/checkpatch.pl tells me:

ERROR: do not initialise statics to 0 or NULL
#95: FILE: net/ipv4/tcp.c:2977:
+static struct tcp_cookie_secret *tcp_secret_generating = NULL;

They need to be NULL, and I'm not planning on exporting them, so what's
the preferred mechanism?

(I've grep'd many other instances of statics = 0 or NULL, so I'm not alone.)