nfsd4: define nfsd4_secinfo_no_name_release()

Commit 34b1744c ("nfsd4: define ->op_release for compound ops")
defined a couple ->op_release functions and run them if necessary.

But there's a problem with that is that it reused
nfsd4_secinfo_release() as the op_release of OP_SECINFO_NO_NAME, and
caused a leak on struct nfsd4_secinfo_no_name in
nfsd4_encode_secinfo_no_name(), because there's no .si_exp field in
struct nfsd4_secinfo_no_name.

I found this because I was unable to umount an ext4 partition after
exporting it via NFS & run fsstress on the nfs mount. A simplified
reproducer would be:

 # mount a local-fs device at /mnt/test, and export it via NFS with
 # fsid=0 export option (this is required)
 mount /dev/sda5 /mnt/test
 echo "/mnt/test *(rw,no_root_squash,fsid=0)" >> /etc/exports
 service nfs restart

 # locally mount the nfs export with all default, note that I have
 # nfsv4.1 configured as the default nfs version, because of the
 # fsid export option, v4 mount would fail and fall back to v3
 mount localhost:/mnt/test /mnt/nfs

 # try to umount the underlying device, but got EBUSY
 umount /mnt/nfs
 service nfs stop
 umount /mnt/test <=== EBUSY here

Fixed it by defining a separate nfsd4_secinfo_no_name_release()
function as the op_release method of OP_SECINFO_NO_NAME that
releases the correct nfsd4_secinfo_no_name structure.

Fixes: 34b1744c ("nfsd4: define ->op_release for compound ops")
Signed-off-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -927,6 +927,13 @@ nfsd4_secinfo_release(union nfsd4_op_u *u)
 		exp_put(u->secinfo.si_exp);
 }
 
+static void
+nfsd4_secinfo_no_name_release(union nfsd4_op_u *u)
+{
+	if (u->secinfo_no_name.sin_exp)
+		exp_put(u->secinfo_no_name.sin_exp);
+}
+
 static __be32
 nfsd4_setattr(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	      union nfsd4_op_u *u)
@@ -2375,7 +2382,7 @@ static const struct nfsd4_operation nfsd4_ops[] = {
 	},
 	[OP_SECINFO_NO_NAME] = {
 		.op_func = nfsd4_secinfo_no_name,
-		.op_release = nfsd4_secinfo_release,
+		.op_release = nfsd4_secinfo_no_name_release,
 		.op_flags = OP_HANDLES_WRONGSEC,
 		.op_name = "OP_SECINFO_NO_NAME",
 		.op_rsize_bop = nfsd4_secinfo_rsize,