SERVER-24316 Add lock conversion cancellation unit-test

This change adds a unit-test to ensure that upgrade from 'weak mode' to
'strong mode' preserves the grant counts correctly. It also tightens the
assertions around lock mode conversion.

2 files changed, 37 insertions, 1 deletions

diff --git a/src/mongo/db/concurrency/lock_manager.cpp b/src/mongo/db/concurrency/lock_manager.cpp
index b2b04e788ef..6d2450086fe 100644
--- a/src/mongo/db/concurrency/lock_manager.cpp
+++ b/src/mongo/db/concurrency/lock_manager.cpp
@@ -619,6 +619,7 @@ bool LockManager::unlock(LockRequest* request) {
     } else if (request->status == LockRequest::STATUS_CONVERTING) {
         // This cancels a pending convert request
         invariant(request->recursiveCount > 0);
+        invariant(lock->conversionsCount > 0);
 
         // Lock only goes from GRANTED to CONVERTING, so cancelling the conversion request
         // brings it back to the previous granted mode.
diff --git a/src/mongo/db/concurrency/lock_manager_test.cpp b/src/mongo/db/concurrency/lock_manager_test.cpp
index aa2edef04b4..218dd6227ad 100644
--- a/src/mongo/db/concurrency/lock_manager_test.cpp
+++ b/src/mongo/db/concurrency/lock_manager_test.cpp
@@ -414,7 +414,42 @@ TEST(LockManager, ConflictCancelMultipleWaiting) {
     lockMgr.unlock(&request[0]);
 }
 
-TEST(LockManager, ConflictCancelWaitingConversion) {
+TEST(LockManager, CancelWaitingConversionWeakModes) {
+    LockManager lockMgr;
+    const ResourceId resId(RESOURCE_COLLECTION, std::string("TestDB.collection"));
+
+    MMAPV1LockerImpl locker1;
+    MMAPV1LockerImpl locker2;
+
+    LockRequestCombo request1(&locker1);
+    LockRequestCombo request2(&locker2);
+
+    // First request granted right away
+    ASSERT(LOCK_OK == lockMgr.lock(resId, &request1, MODE_IS));
+    ASSERT(request1.numNotifies == 0);
+
+    // Second request is granted right away
+    ASSERT(LOCK_OK == lockMgr.lock(resId, &request2, MODE_IX));
+    ASSERT(request2.numNotifies == 0);
+
+    // Convert first request to conflicting
+    ASSERT(LOCK_WAITING == lockMgr.convert(resId, &request1, MODE_S));
+    ASSERT(request1.mode == MODE_IS);
+    ASSERT(request1.convertMode == MODE_S);
+    ASSERT(request1.numNotifies == 0);
+
+    // Cancel the conflicting conversion
+    lockMgr.unlock(&request1);
+    ASSERT(request1.mode == MODE_IS);
+    ASSERT(request1.convertMode == MODE_NONE);
+    ASSERT(request1.numNotifies == 0);
+
+    // Free the remaining locks so the LockManager destructor does not complain
+    lockMgr.unlock(&request1);
+    lockMgr.unlock(&request2);
+}
+
+TEST(LockManager, CancelWaitingConversionStrongModes) {
     LockManager lockMgr;
     const ResourceId resId(RESOURCE_COLLECTION, std::string("TestDB.collection"));