[GitHub] [zookeeper] sonatype-lift[bot] commented on a diff in pull request #1993: ZOOKEEPER-4646: Committed txns may still be lost if followers crash after replying ACK of NEWLEADER but before writing txns to disk

Sun, 26 Mar 2023 10:42:13 -0700 


sonatype-lift[bot] commented on code in PR #1993:
URL: https://github.com/apache/zookeeper/pull/1993#discussion_r1148603332


##########
zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java:
##########
@@ -781,6 +806,13 @@ protected void syncWithLeader(long newLeaderZxid) throws 
Exception {
 
         // We need to log the stuff that came in between the snapshot and the 
uptodate
         if (zk instanceof FollowerZooKeeperServer) {
+            // Reply queued ACKs that are generated before replying ACK of 
NEWLEADER
+            for (QuorumPacket p : queuedAcksInSync) {

Review Comment:
   <picture><img alt="6% of developers fix this issue" 
src="https://lift.sonatype.com/api/commentimage/fixrate/6/display.svg";></picture>
   
   <b>*THREAD_SAFETY_VIOLATION:</b>*  Read/Write race. Non-private method 
`Learner.syncWithLeader(...)` reads without synchronization from container 
`this.queuedAcksInSync` via call to `ConcurrentLinkedQueue.iterator()`. 
Potentially races with write in method `Learner.addQueuedAcksInSync(...)`.
    Reporting because this access may occur on a background thread.
   
   ❗❗ <b>2 similar findings have been found in this PR</b>
   
   <details><summary>🔎 Expand here to view all instances of this 
finding</summary><br/>
     
     
   <div align=\"center\">
   
   
   | **File Path** | **Line Number** |
   | ------------- | ------------- |
   | 
zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java 
| 
[128](https://github.com/apache/zookeeper/blob/0dca8ef9e6ba391936b0029e1ecdb657e2e878ae/zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java#L128)
 |
   | 
zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java 
| 
[814](https://github.com/apache/zookeeper/blob/0dca8ef9e6ba391936b0029e1ecdb657e2e878ae/zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java#L814)
 |
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