From 2dbbe6ce85a464fcfa047237e7fb820a6f8a8f34 Mon Sep 17 00:00:00 2001
From: Ted Yu <yuzhihong@gmail.com>
Date: Sat, 9 May 2020 16:28:47 -0700
Subject: [PATCH] mvcc: Obtain txLock once in readTx#UnsafeRange

Signed-off-by: Ted Yu <yuzhihong@gmail.com>
---
 mvcc/backend/read_tx.go | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mvcc/backend/read_tx.go b/mvcc/backend/read_tx.go
index 91fe72ec5..fcca9f089 100644
--- a/mvcc/backend/read_tx.go
+++ b/mvcc/backend/read_tx.go
@@ -77,18 +77,25 @@ func (rt *readTx) UnsafeRange(bucketName, key, endKey []byte, limit int64) ([][]
 	rt.txMu.RLock()
 	bucket, ok := rt.buckets[bn]
 	rt.txMu.RUnlock()
+	lockHeld := false
 	if !ok {
 		rt.txMu.Lock()
+		lockHeld = true
 		bucket = rt.tx.Bucket(bucketName)
 		rt.buckets[bn] = bucket
-		rt.txMu.Unlock()
 	}
 
 	// ignore missing bucket since may have been created in this batch
 	if bucket == nil {
+		if lockHeld {
+			rt.txMu.Unlock()
+		}
 		return keys, vals
 	}
-	rt.txMu.Lock()
+	if !lockHeld {
+		rt.txMu.Lock()
+		lockHeld = true
+	}
 	c := bucket.Cursor()
 	rt.txMu.Unlock()