sync: detect double lock from the same thread

Double lock of the same (non-recursive) mutex from the same thread
is producing an undefined behavior. Detect this from DEBUG_LOCKORDER
and react similarly to the deadlock detection.

src/sync.cpp

@@ -20,6 +20,7 @@
 #include <set>
 #include <system_error>
 #include <thread>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <vector>
@@ -138,17 +139,50 @@ static void potential_deadlock_detected(const LockPair& mismatch, const LockStac
     throw std::logic_error(strprintf("potential deadlock detected: %s -> %s -> %s", mutex_b, mutex_a, mutex_b));
 }
 
+static void double_lock_detected(const void* mutex, LockStack& lock_stack)
+{
+    LogPrintf("DOUBLE LOCK DETECTED\n");
+    LogPrintf("Lock order:\n");
+    for (const LockStackItem& i : lock_stack) {
+        if (i.first == mutex) {
+            LogPrintf(" (*)"); /* Continued */
+        }
+        LogPrintf(" %s\n", i.second.ToString());
+    }
+    if (g_debug_lockorder_abort) {
+        tfm::format(std::cerr, "Assertion failed: detected double lock at %s:%i, details in debug log.\n", __FILE__, __LINE__);
+        abort();
+    }
+    throw std::logic_error("double lock detected");
+}
+
 template <typename MutexType>
 static void push_lock(MutexType* c, const CLockLocation& locklocation)
 {
+    constexpr bool is_recursive_mutex =
+        std::is_base_of<RecursiveMutex, MutexType>::value ||
+        std::is_base_of<std::recursive_mutex, MutexType>::value;
+
     LockData& lockdata = GetLockData();
     std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
     LockStack& lock_stack = lockdata.m_lock_stacks[std::this_thread::get_id()];
     lock_stack.emplace_back(c, locklocation);
-    for (const LockStackItem& i : lock_stack) {
-        if (i.first == c)
-            break;
+    for (size_t j = 0; j < lock_stack.size() - 1; ++j) {
+        const LockStackItem& i = lock_stack[j];
+        if (i.first == c) {
+            if (is_recursive_mutex) {
+                break;
+            }
+            // It is not a recursive mutex and it appears in the stack two times:
+            // at position `j` and at the end (which we added just before this loop).
+            // Can't allow locking the same (non-recursive) mutex two times from the
+            // same thread as that results in an undefined behavior.
+            auto lock_stack_copy = lock_stack;
+            lock_stack.pop_back();
+            double_lock_detected(c, lock_stack_copy);
+            // double_lock_detected() does not return.
+        }
 
         const LockPair p1 = std::make_pair(i.first, c);
         if (lockdata.lockorders.count(p1))