From c4a4f082a3b9a83bed69a86af53a0a905b9e287b Mon Sep 17 00:00:00 2001
From: Jordi Serra Torrens <jordi.serra-torrens@mongodb.com>
Date: Fri, 20 Oct 2023 15:26:05 +0000
Subject: [PATCH] Repro SERVER-82353

---
 jstests/noPassthrough/foo.js      | 55 +++++++++++++++++++++++++++++++
 src/mongo/s/commands/strategy.cpp |  2 ++
 2 files changed, 57 insertions(+)
 create mode 100644 jstests/noPassthrough/foo.js

diff --git a/jstests/noPassthrough/foo.js b/jstests/noPassthrough/foo.js
new file mode 100644
index 00000000000..b2397d27ac9
--- /dev/null
+++ b/jstests/noPassthrough/foo.js
@@ -0,0 +1,55 @@
+import {configureFailPoint} from "jstests/libs/fail_point_util.js";
+
+(function() {
+'use strict';
+const dbName = 'test';
+const collName = 'foo';
+const ns = dbName + '.' + collName;
+
+const st = new ShardingTest({mongos: 1, shards: 2});
+
+st.adminCommand({enableSharding: dbName, primaryShard: st.shard0.shardName});
+
+const coll = st.getDB(dbName)[collName];
+coll.insert({x: 1, c: 0});
+
+// Set a failpoint that will block transactions on mongos right after if has chosen their
+// 'atClusterTime'.
+const mongos = st.s;
+let fp = configureFailPoint(mongos, 'hangAfterSettingTransactionDefaultAtClusterTime');
+
+// Start multi-document txn that will increment 'c' by one for the document with x=1.
+let awaitResult = startParallelShell(() => {
+    let session = db.getMongo().startSession();
+    let coll = session.getDatabase('test')['foo'];
+
+    session.startTransaction({readConcern: {level: 'snapshot'}});
+    const updateResult = assert.commandWorked(coll.update({x: 1}, {$inc: {c: 1}}));
+
+    // Note: We'd expect one document to have been updated. But because of the bug being repro'd
+    // here, none was!
+    jsTest.log("--DEBUG-- updateResult: " + tojson(updateResult));
+    // assert.eq(1, updateResult.nModified);
+
+    // We'd also expect a find within the transaction to see the documents, but it doesn't.
+    // assert.eq(1, coll.find().itcount());
+
+    session.commitTransaction();
+}, mongos.port);
+
+// Wait to hit the failpoint on mongos.
+fp.wait();
+
+// Run movePrimary.
+assert.commandWorked(mongos.adminCommand({movePrimary: dbName, to: st.shard1.shardName}));
+
+// Unset the failpoint.
+fp.off();
+awaitResult();
+
+// Check document 'c' has been incremented to 1.
+// Note: Because of the bug being repro'd, it Will fail here.
+assert.eq(1, coll.findOne({x: 1}).c);
+
+st.stop();
+})();
diff --git a/src/mongo/s/commands/strategy.cpp b/src/mongo/s/commands/strategy.cpp
index a643d23f06d..2f60c6ce34a 100644
--- a/src/mongo/s/commands/strategy.cpp
+++ b/src/mongo/s/commands/strategy.cpp
@@ -129,6 +129,7 @@ namespace mongo {
 namespace {
 
 MONGO_FAIL_POINT_DEFINE(hangBeforeCheckingMongosShutdownInterrupt);
+MONGO_FAIL_POINT_DEFINE(hangAfterSettingTransactionDefaultAtClusterTime);
 const auto kOperationTime = "operationTime"_sd;
 
 /**
@@ -208,6 +209,7 @@ Future<void> invokeInTransactionRouter(TransactionRouter::Router& txnRouter,
                                        std::shared_ptr<CommandInvocation> invocation) {
     auto opCtx = rec->getOpCtx();
     txnRouter.setDefaultAtClusterTime(opCtx);
+    hangAfterSettingTransactionDefaultAtClusterTime.pauseWhileSet();
 
     return runCommandInvocation(rec, std::move(invocation))
         .tapError([rec = std::move(rec)](Status status) {
-- 
2.34.1