From 129dadf4d0d90c8d7288d4e60cec511e725453fa Mon Sep 17 00:00:00 2001
From: wjHuang <huangwenjun1997@gmail.com>
Date: Wed, 23 Feb 2022 16:41:43 +0800
Subject: [PATCH] ddl: fix data race for ddl seq (#32542)

close pingcap/tidb#32541
---
 ddl/ddl.go        | 11 ++++++++---
 ddl/ddl_worker.go | 21 ++++++++++-----------
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/ddl/ddl.go b/ddl/ddl.go
index 48e9d5042a..b66e9fd0c4 100644
--- a/ddl/ddl.go
+++ b/ddl/ddl.go
@@ -217,6 +217,11 @@ type ddlCtx struct {
 		hook        Callback
 		interceptor Interceptor
 	}
+
+	ddlSeqNumMu struct {
+		sync.Mutex
+		seqNum uint64
+	}
 }
 
 func (dc *ddlCtx) isOwner() bool {
@@ -379,8 +384,8 @@ func (d *ddl) Start(ctxPool *pools.ResourcePool) error {
 		d.workers = make(map[workerType]*worker, 2)
 		d.sessPool = newSessionPool(ctxPool)
 		d.delRangeMgr = d.newDeleteRangeManager(ctxPool == nil)
-		d.workers[generalWorker] = newWorker(d.ctx, generalWorker, d.sessPool, d.delRangeMgr)
-		d.workers[addIdxWorker] = newWorker(d.ctx, addIdxWorker, d.sessPool, d.delRangeMgr)
+		d.workers[generalWorker] = newWorker(d.ctx, generalWorker, d.sessPool, d.delRangeMgr, d.ddlCtx)
+		d.workers[addIdxWorker] = newWorker(d.ctx, addIdxWorker, d.sessPool, d.delRangeMgr, d.ddlCtx)
 		for _, worker := range d.workers {
 			worker.wg.Add(1)
 			w := worker
@@ -395,7 +400,7 @@ func (d *ddl) Start(ctxPool *pools.ResourcePool) error {
 
 		err = kv.RunInNewTxn(d.ctx, d.store, true, func(ctx context.Context, txn kv.Transaction) error {
 			t := meta.NewMeta(txn)
-			globalSeqNum, err = t.GetHistoryDDLCount()
+			d.ddlSeqNumMu.seqNum, err = t.GetHistoryDDLCount()
 			return err
 		})
 		if err != nil {
diff --git a/ddl/ddl_worker.go b/ddl/ddl_worker.go
index 7885009b71..ae0348efd2 100644
--- a/ddl/ddl_worker.go
+++ b/ddl/ddl_worker.go
@@ -53,9 +53,6 @@ var (
 	ddlWorkerID = int32(0)
 	// WaitTimeWhenErrorOccurred is waiting interval when processing DDL jobs encounter errors.
 	WaitTimeWhenErrorOccurred = int64(1 * time.Second)
-
-	ddlSeqNumMu  sync.Mutex
-	globalSeqNum uint64
 )
 
 // GetWaitTimeWhenErrorOccurred return waiting interval when processing DDL jobs encounter errors.
@@ -97,6 +94,7 @@ type worker struct {
 	logCtx          context.Context
 	lockSeqNum      bool
 
+	*ddlCtx
 	ddlJobCache
 }
 
@@ -109,7 +107,7 @@ type ddlJobCache struct {
 	cacheDigest        *parser.Digest
 }
 
-func newWorker(ctx context.Context, tp workerType, sessPool *sessionPool, delRangeMgr delRangeManager) *worker {
+func newWorker(ctx context.Context, tp workerType, sessPool *sessionPool, delRangeMgr delRangeManager, dCtx *ddlCtx) *worker {
 	worker := &worker{
 		id:       atomic.AddInt32(&ddlWorkerID, 1),
 		tp:       tp,
@@ -121,6 +119,7 @@ func newWorker(ctx context.Context, tp workerType, sessPool *sessionPool, delRan
 			cacheNormalizedSQL: "",
 			cacheDigest:        nil,
 		},
+		ddlCtx:          dCtx,
 		reorgCtx:        &reorgCtx{notifyCancelReorgJob: 0},
 		sessPool:        sessPool,
 		delRangeManager: delRangeMgr,
@@ -450,10 +449,10 @@ func (w *worker) finishDDLJob(t *meta.Meta, job *model.Job) (err error) {
 }
 
 func (w *worker) writeDDLSeqNum(job *model.Job) {
-	ddlSeqNumMu.Lock()
+	w.ddlSeqNumMu.Lock()
+	w.ddlSeqNumMu.seqNum++
 	w.lockSeqNum = true
-	globalSeqNum++
-	job.SeqNum = globalSeqNum
+	job.SeqNum = w.ddlSeqNumMu.seqNum
 }
 
 func finishRecoverTable(w *worker, job *model.Job) error {
@@ -605,10 +604,10 @@ func (w *worker) handleDDLJobQueue(d *ddlCtx) error {
 
 		if err != nil {
 			if w.lockSeqNum {
-				// txn commit failed, we should reset globalSeqNum
-				globalSeqNum--
+				// txn commit failed, we should reset seqNum.
+				w.ddlSeqNumMu.seqNum--
 				w.lockSeqNum = false
-				ddlSeqNumMu.Unlock()
+				w.ddlSeqNumMu.Unlock()
 			}
 			return errors.Trace(err)
 		} else if job == nil {
@@ -617,7 +616,7 @@ func (w *worker) handleDDLJobQueue(d *ddlCtx) error {
 		}
 		if w.lockSeqNum {
 			w.lockSeqNum = false
-			ddlSeqNumMu.Unlock()
+			d.ddlSeqNumMu.Unlock()
 		}
 		w.waitDependencyJobFinished(job, &waitDependencyJobCnt)