diff --git a/blockchain/v0/reactor.go b/blockchain/v0/reactor.go
index 50f2e164e..dd3878669 100644
--- a/blockchain/v0/reactor.go
+++ b/blockchain/v0/reactor.go
@@ -204,6 +204,8 @@ func (bcR *BlockchainReactor) respondToPeer(msg *bcproto.BlockRequest,
 }
 
 // Receive implements Reactor by handling 4 types of messages (look below).
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (bcR *BlockchainReactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	msg, err := bc.DecodeMsg(msgBytes)
 	if err != nil {
diff --git a/blockchain/v1/reactor.go b/blockchain/v1/reactor.go
index c16139153..78ce71e18 100644
--- a/blockchain/v1/reactor.go
+++ b/blockchain/v1/reactor.go
@@ -250,6 +250,8 @@ func (bcR *BlockchainReactor) RemovePeer(peer p2p.Peer, reason interface{}) {
 }
 
 // Receive implements Reactor by handling 4 types of messages (look below).
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (bcR *BlockchainReactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	msg, err := bc.DecodeMsg(msgBytes)
 	if err != nil {
diff --git a/blockchain/v2/reactor.go b/blockchain/v2/reactor.go
index 0c43db179..5da117c94 100644
--- a/blockchain/v2/reactor.go
+++ b/blockchain/v2/reactor.go
@@ -455,6 +455,8 @@ func (r *BlockchainReactor) Stop() error {
 }
 
 // Receive implements Reactor by handling different message types.
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (r *BlockchainReactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	msg, err := bc.DecodeMsg(msgBytes)
 	if err != nil {
diff --git a/consensus/reactor.go b/consensus/reactor.go
index c4a2ef9fd..9fb41c37c 100644
--- a/consensus/reactor.go
+++ b/consensus/reactor.go
@@ -220,6 +220,8 @@ func (conR *Reactor) RemovePeer(peer p2p.Peer, reason interface{}) {
 // Peer state updates can happen in parallel, but processing of
 // proposals, block parts, and votes are ordered by the receiveRoutine
 // NOTE: blocks on consensus state for proposals, block parts, and votes
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (conR *Reactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	if !conR.IsRunning() {
 		conR.Logger.Debug("Receive", "src", src, "chId", chID, "bytes", msgBytes)
diff --git a/evidence/reactor.go b/evidence/reactor.go
index 421e4bc18..951d64d71 100644
--- a/evidence/reactor.go
+++ b/evidence/reactor.go
@@ -66,6 +66,8 @@ func (evR *Reactor) AddPeer(peer p2p.Peer) {
 
 // Receive implements Reactor.
 // It adds any received evidence to the evpool.
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (evR *Reactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	evis, err := decodeMsg(msgBytes)
 	if err != nil {
diff --git a/mempool/reactor.go b/mempool/reactor.go
index b4f76b9e8..6bf0ce7d7 100644
--- a/mempool/reactor.go
+++ b/mempool/reactor.go
@@ -160,6 +160,8 @@ func (memR *Reactor) RemovePeer(peer p2p.Peer, reason interface{}) {
 
 // Receive implements Reactor.
 // It adds any received transactions to the mempool.
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (memR *Reactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	msg, err := memR.decodeMsg(msgBytes)
 	if err != nil {
diff --git a/p2p/base_reactor.go b/p2p/base_reactor.go
index 86b0d980a..59faf4c3f 100644
--- a/p2p/base_reactor.go
+++ b/p2p/base_reactor.go
@@ -44,6 +44,9 @@ type Reactor interface {
 	// copying.
 	//
 	// CONTRACT: msgBytes are not nil.
+	//
+	// XXX: do not call any methods that can block or incur heavy processing.
+	// https://github.com/tendermint/tendermint/issues/2888
 	Receive(chID byte, peer Peer, msgBytes []byte)
 }
 
diff --git a/p2p/pex/pex_reactor.go b/p2p/pex/pex_reactor.go
index 71b71b054..fc701bfdd 100644
--- a/p2p/pex/pex_reactor.go
+++ b/p2p/pex/pex_reactor.go
@@ -236,6 +236,8 @@ func (r *Reactor) logErrAddrBook(err error) {
 }
 
 // Receive implements Reactor by handling incoming PEX messages.
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (r *Reactor) Receive(chID byte, src Peer, msgBytes []byte) {
 	msg, err := decodeMsg(msgBytes)
 	if err != nil {
diff --git a/statesync/reactor.go b/statesync/reactor.go
index 4f4310f84..0abd91cf1 100644
--- a/statesync/reactor.go
+++ b/statesync/reactor.go
@@ -90,6 +90,8 @@ func (r *Reactor) RemovePeer(peer p2p.Peer, reason interface{}) {
 }
 
 // Receive implements p2p.Reactor.
+// XXX: do not call any methods that can block or incur heavy processing.
+// https://github.com/tendermint/tendermint/issues/2888
 func (r *Reactor) Receive(chID byte, src p2p.Peer, msgBytes []byte) {
 	if !r.IsRunning() {
 		return