Merge #19340: Preserve the `LockData` initial state if "potential deadlock detected" exception thrown

63e9e40b73507b0c9361fc8728d4e97fd72c9ec9 test: Add LockStackEmpty() (Hennadii Stepanov)
42b2a953735457cbf7b62a18b89811a66e573298 test: Repeat deadlock tests (Hennadii Stepanov)
1f96be25b020a56afa330286ee4f241aa14d3983 Preserve initial state if push_lock() throws exception (Hennadii Stepanov)

Pull request description:

  On master (e3fa3c7d671e34038a262bb2db16b30bee82153d) if the `push_lock()` throws the "potential deadlock detected" exception (via the `potential_deadlock_detected()` call), the `LockData` instance internal state differs from one when the `push_lock()` was called. This non-well behaviour makes (at least) testing brittle.

  This PR preserves the `LockData` instance initial state if `push_lock()` throws an exception, and improves the `sync_tests` unit test.

ACKs for top commit:
  MarcoFalke:
    re-ACK 63e9e40b73
  vasild:
    ACK 63e9e40

Tree-SHA512: 7679182154ce5f079b44b790faf76eb5f553328dea70a326ff6b600db70e2f9ae015a33a104ca070cb660318280cb79b6b42e37ea5166f26f9e627ba721fcdec

1 files changed, 19 insertions, 3 deletions

diff --git a/src/sync.cpp b/src/sync.cpp
index 10f0483189..4be13a3c48 100644
--- a/src/sync.cpp
+++ b/src/sync.cpp
@@ -149,12 +149,17 @@ static void push_lock(void* c, const CLockLocation& locklocation)
         const LockPair p1 = std::make_pair(i.first, c);
         if (lockdata.lockorders.count(p1))
             continue;
-        lockdata.lockorders.emplace(p1, lock_stack);
 
         const LockPair p2 = std::make_pair(c, i.first);
+        if (lockdata.lockorders.count(p2)) {
+            auto lock_stack_copy = lock_stack;
+            lock_stack.pop_back();
+            potential_deadlock_detected(p1, lockdata.lockorders[p2], lock_stack_copy);
+            // potential_deadlock_detected() does not return.
+        }
+
+        lockdata.lockorders.emplace(p1, lock_stack);
         lockdata.invlockorders.insert(p2);
-        if (lockdata.lockorders.count(p2))
-            potential_deadlock_detected(p1, lockdata.lockorders[p2], lockdata.lockorders[p1]);
     }
 }
 
@@ -259,6 +264,17 @@ void DeleteLock(void* cs)
     }
 }
 
+bool LockStackEmpty()
+{
+    LockData& lockdata = GetLockData();
+    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
+    const auto it = lockdata.m_lock_stacks.find(std::this_thread::get_id());
+    if (it == lockdata.m_lock_stacks.end()) {
+        return true;
+    }
+    return it->second.empty();
+}
+
 bool g_debug_lockorder_abort = true;
 
 #endif /* DEBUG_LOCKORDER */