NFSD: fix leaked reference count of nfsd4_ssc_umount_item

The reference count of nfsd4_ssc_umount_item is not decremented
on error conditions. This prevents the laundromat from unmounting
the vfsmount of the source file.

This patch decrements the reference count of nfsd4_ssc_umount_item
on error.

Fixes: f4e44b39 ("NFSD: delay unmount source's export after inter-server copy completed.")
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4proc.c

@@ -1813,13 +1813,17 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	release_copy_files(copy);
 	return status;
 out_err:
+	if (nfsd4_ssc_is_inter(copy)) {
+		/*
+		 * Source's vfsmount of inter-copy will be unmounted
+		 * by the laundromat. Use copy instead of async_copy
+		 * since async_copy->ss_nsui might not be set yet.
+		 */
+		refcount_dec(&copy->ss_nsui->nsui_refcnt);
+	}
 	if (async_copy)
 		cleanup_async_copy(async_copy);
 	status = nfserrno(-ENOMEM);
-	/*
-	 * source's vfsmount of inter-copy will be unmounted
-	 * by the laundromat
-	 */
 	goto out;
 }