From 8d3c36ccc3197f58cf5f91d0cf095b2ad20e06df Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Thu, 18 Feb 2021 08:36:05 -0500
Subject: [PATCH] abci: Fix ReCheckTx for Socket Client (bp #6124) (#6125)

---
 CHANGELOG_PENDING.md         |  1 +
 abci/client/client.go        | 60 +++++++++++++++++++++---------------
 abci/client/socket_client.go |  4 +--
 3 files changed, 38 insertions(+), 27 deletions(-)

diff --git a/CHANGELOG_PENDING.md b/CHANGELOG_PENDING.md
index 31beb85c4..9f086503a 100644
--- a/CHANGELOG_PENDING.md
+++ b/CHANGELOG_PENDING.md
@@ -24,3 +24,4 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 
 ### BUG FIXES
 
+- [ABCI] \#6124 Fixes a panic condition during callback execution in `ReCheckTx` during high tx load. (@alexanderbez)
diff --git a/abci/client/client.go b/abci/client/client.go
index 09583327a..c5c1ab219 100644
--- a/abci/client/client.go
+++ b/abci/client/client.go
@@ -74,12 +74,8 @@ func NewClient(addr, transport string, mustConnect bool) (client Client, err err
 	return
 }
 
-//----------------------------------------
-
 type Callback func(*types.Request, *types.Response)
 
-//----------------------------------------
-
 type ReqRes struct {
 	*types.Request
 	*sync.WaitGroup
@@ -101,34 +97,50 @@ func NewReqRes(req *types.Request) *ReqRes {
 	}
 }
 
-// Sets the callback for this ReqRes atomically.
-// If reqRes is already done, calls cb immediately.
-// NOTE: reqRes.cb should not change if reqRes.done.
-// NOTE: only one callback is supported.
-func (reqRes *ReqRes) SetCallback(cb func(res *types.Response)) {
-	reqRes.mtx.Lock()
+// Sets sets the callback. If reqRes is already done, it will call the cb
+// immediately. Note, reqRes.cb should not change if reqRes.done and only one
+// callback is supported.
+func (r *ReqRes) SetCallback(cb func(res *types.Response)) {
+	r.mtx.Lock()
 
-	if reqRes.done {
-		reqRes.mtx.Unlock()
-		cb(reqRes.Response)
+	if r.done {
+		r.mtx.Unlock()
+		cb(r.Response)
 		return
 	}
 
-	reqRes.cb = cb
-	reqRes.mtx.Unlock()
+	r.cb = cb
+	r.mtx.Unlock()
 }
 
-func (reqRes *ReqRes) GetCallback() func(*types.Response) {
-	reqRes.mtx.Lock()
-	defer reqRes.mtx.Unlock()
-	return reqRes.cb
+// InvokeCallback invokes a thread-safe execution of the configured callback
+// if non-nil.
+func (r *ReqRes) InvokeCallback() {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
+
+	if r.cb != nil {
+		r.cb(r.Response)
+	}
 }
 
-// NOTE: it should be safe to read reqRes.cb without locks after this.
-func (reqRes *ReqRes) SetDone() {
-	reqRes.mtx.Lock()
-	reqRes.done = true
-	reqRes.mtx.Unlock()
+// GetCallback returns the configured callback of the ReqRes object which may be
+// nil. Note, it is not safe to concurrently call this in cases where it is
+// marked done and SetCallback is called before calling GetCallback as that
+// will invoke the callback twice and create a potential race condition.
+//
+// ref: https://github.com/tendermint/tendermint/issues/5439
+func (r *ReqRes) GetCallback() func(*types.Response) {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
+	return r.cb
+}
+
+// SetDone marks the ReqRes object as done.
+func (r *ReqRes) SetDone() {
+	r.mtx.Lock()
+	r.done = true
+	r.mtx.Unlock()
 }
 
 func waitGroup1() (wg *sync.WaitGroup) {
diff --git a/abci/client/socket_client.go b/abci/client/socket_client.go
index 1e6a47801..a369f878c 100644
--- a/abci/client/socket_client.go
+++ b/abci/client/socket_client.go
@@ -212,9 +212,7 @@ func (cli *socketClient) didRecvResponse(res *types.Response) error {
 	//
 	// NOTE: It is possible this callback isn't set on the reqres object. At this
 	// point, in which case it will be called after, when it is set.
-	if cb := reqres.GetCallback(); cb != nil {
-		cb(res)
-	}
+	reqres.InvokeCallback()
 
 	return nil
 }