avoid source index to be same as destination index (#20238)

during rebalance stop, it can possibly happen that
Put() would race by overwriting the same object again.

This may very well if done "successfully" it can
potentially proceed to delete the object from the pool,
causing data loss.

This PR enhances #20233 to handle more scenarios such
as these.

cmd/erasure-server-pool.go

@@ -1147,6 +1147,16 @@ func (z *erasureServerPools) DeleteObject(ctx context.Context, bucket string, ob
 		return pinfo.ObjInfo, nil
 	}
 
+	// Datamovement must never be allowed on the same pool.
+	if opts.DataMovement && opts.SrcPoolIdx == pinfo.Index {
+		return pinfo.ObjInfo, DataMovementOverwriteErr{
+			Bucket:    bucket,
+			Object:    object,
+			VersionID: opts.VersionID,
+			Err:       errDataMovementSrcDstPoolSame,
+		}
+	}
+
 	// Delete concurrently in all server pools with read quorum error for unversioned objects.
 	if len(noReadQuorumPools) > 0 && !opts.Versioned && !opts.VersionSuspended {
 		return z.deleteObjectFromAllPools(ctx, bucket, object, opts, noReadQuorumPools)
@@ -2797,5 +2807,14 @@ func (z *erasureServerPools) DecomTieredObject(ctx context.Context, bucket, obje
 		return err
 	}
 
+	if opts.DataMovement && idx == opts.SrcPoolIdx {
+		return DataMovementOverwriteErr{
+			Bucket:    bucket,
+			Object:    object,
+			VersionID: opts.VersionID,
+			Err:       errDataMovementSrcDstPoolSame,
+		}
+	}
+
 	return z.serverPools[idx].DecomTieredObject(ctx, bucket, object, fi, opts)
 }