use of V_tcbinfo lock for TCP syncache

[Vijay Singh]

As it is today, a socket upcall on a listener socket is made with the
V_tcbinfo lock held. [tcp_input -> syncache_socket -> sonewconn ->
sowakeup].

I feel that the use of the V_tcbinfo is not consistent in the syncache code.

In syncache_add(), we drop the lock before doing the lookup:

        INP_WUNLOCK(inp);
        INP_INFO_WUNLOCK(&V_tcbinfo);
        [..snip..]
        sc = syncache_lookup(inc, &sch);        /* returns locked entry */

However, when going through syncache_expand() or syncache_chkrst() we
keep the V_tcbinfo lock.

Since the syncache has its own lock, do we need to hold the V_tcbinfo
lock when calling syncache_socket()?

If there are ideas, or patches, I can give them a try.

-vijay