NFSD: Never decrement pending_async_copies on error

The error flow in nfsd4_copy() calls cleanup_async_copy(), which
already decrements nn->pending_async_copies.

Reported-by: Olga Kornievskaia <okorniev@redhat.com>
Fixes: aadc3bb ("NFSD: Limit the number of concurrent async COPY operations")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4proc.c

@@ -1845,10 +1845,8 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		refcount_set(&async_copy->refcount, 1);
 		/* Arbitrary cap on number of pending async copy operations */
 		if (atomic_inc_return(&nn->pending_async_copies) >
-				(int)rqstp->rq_pool->sp_nrthreads) {
-			atomic_dec(&nn->pending_async_copies);
+				(int)rqstp->rq_pool->sp_nrthreads)
 			goto out_err;
-		}
 		async_copy->cp_src = kmalloc(sizeof(*async_copy->cp_src), GFP_KERNEL);
 		if (!async_copy->cp_src)
 			goto out_err;