nfsd41: free_session/free_client must be called under the client_lock

The session client is manipulated under the client_lock hence
both free_session and nfsd4_del_conns must be called under this lock.

This patch adds a BUG_ON that checks this condition in the
respective functions and implements the missing locks.

nfsd4_{get,put}_session helpers were moved to the C file that uses them
so to prevent use from external files and an unlocked version of
nfsd4_put_session is provided for external use from nfs4xdr.c

Signed-off-by: Benny Halevy <bhalevy@tonian.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/state.h

@@ -198,18 +198,7 @@ struct nfsd4_session {
 	struct nfsd4_slot	*se_slots[];	/* forward channel slots */
 };
 
-static inline void
-nfsd4_put_session(struct nfsd4_session *ses)
-{
-	extern void free_session(struct kref *kref);
-	kref_put(&ses->se_ref, free_session);
-}
-
-static inline void
-nfsd4_get_session(struct nfsd4_session *ses)
-{
-	kref_get(&ses->se_ref);
-}
+extern void nfsd4_put_session(struct nfsd4_session *ses);
 
 /* formatted contents of nfs4_sessionid */
 struct nfsd4_sessionid {