nfsd: use nfsd_v4client() in nfsd_breaker_owns_lease()

nfsd_breaker_owns_lease() currently open-codes the same test that
nfsd_v4client() performs.

With this patch we use nfsd_v4client() instead.

Also as i_am_nfsd() is only used in combination with kthread_data(),
replace it with nfsd_current_rqst() which combines the two and returns a
valid svc_rqst, or NULL.

The test for NULL is moved into nfsd_v4client() for code clarity.
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -5277,11 +5277,8 @@ static bool nfsd_breaker_owns_lease(struct file_lease *fl)
 	struct svc_rqst *rqst;
 	struct nfs4_client *clp;
 
-	if (!i_am_nfsd())
-		return false;
-	rqst = kthread_data(current);
-	/* Note rq_prog == NFS_ACL_PROGRAM is also possible: */
-	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
+	rqst = nfsd_current_rqst();
+	if (!nfsd_v4client(rqst))
 		return false;
 	clp = *(rqst->rq_lease_breaker);
 	return dl->dl_stid.sc_client == clp;

fs/nfsd/nfsd.h

@@ -118,7 +118,7 @@ int		nfsd_get_nrthreads(int n, int *, struct net *);
 int		nfsd_set_nrthreads(int n, int *, struct net *);
 void		nfsd_shutdown_threads(struct net *net);
 
-bool		i_am_nfsd(void);
+struct svc_rqst *nfsd_current_rqst(void);
 
 struct nfsdfs_client {
 	struct kref cl_ref;
@@ -159,7 +159,7 @@ extern int nfsd_max_blksize;
 
 static inline int nfsd_v4client(struct svc_rqst *rq)
 {
-	return rq->rq_prog == NFS_PROGRAM && rq->rq_vers == 4;
+	return rq && rq->rq_prog == NFS_PROGRAM && rq->rq_vers == 4;
 }
 static inline struct user_namespace *
 nfsd_user_namespace(const struct svc_rqst *rqstp)

fs/nfsd/nfssvc.c

@@ -578,9 +578,11 @@ void nfsd_shutdown_threads(struct net *net)
 	mutex_unlock(&nfsd_mutex);
 }
 
-bool i_am_nfsd(void)
+struct svc_rqst *nfsd_current_rqst(void)
 {
-	return kthread_func(current) == nfsd;
+	if (kthread_func(current) == nfsd)
+		return kthread_data(current);
+	return NULL;
 }
 
 int nfsd_create_serv(struct net *net)