Revert "NFSD: Force all NFSv4.2 COPY requests to be synchronous"

In the past several kernel releases, we've made NFSv4.2 async copy
reliable:
 - The Linux NFS client and server now both implement and use the
   NFSv4.2 OFFLOAD_STATUS operation
 - The Linux NFS server keeps copy stateids around longer
 - The Linux NFS client and server now both implement referring call
   lists

And resilient against DoS:
 - The Linux NFS server limits the number of concurrent async copy
   operations

Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

Author: chucklever

fs/nfsd/nfs4proc.c

@@ -1917,13 +1917,6 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	struct nfsd42_write_res *result;
 	__be32 status;
 
-	/*
-	 * Currently, async COPY is not reliable. Force all COPY
-	 * requests to be synchronous to avoid client application
-	 * hangs waiting for COPY completion.
-	 */
-	nfsd4_copy_set_sync(copy, true);
-
 	result = &copy->cp_res;
 	nfsd_copy_write_verifier((__be32 *)&result->wr_verifier.data, nn);