# UNDF: UNDF-2026-000001145
--- a/Core/HLE/sceKernelMutex.cpp
+++ b/Core/HLE/sceKernelMutex.cpp
@@ -547,3 +547,3 @@
 		// May be in a tight loop timing out (where we don't remove from waitingThreads yet), don't want to add duplicates.
-		if (std::find(mutex->waitingThreads.begin(), mutex->waitingThreads.end(), threadID) == mutex->waitingThreads.end())
+		if (mutex->waitingThreadSet.insert(threadID).second)
 			mutex->waitingThreads.push_back(threadID);
@@ -569,3 +569,3 @@
 		// May be in a tight loop timing out (where we don't remove from waitingThreads yet), don't want to add duplicates.
-		if (std::find(mutex->waitingThreads.begin(), mutex->waitingThreads.end(), threadID) == mutex->waitingThreads.end())
+		if (mutex->waitingThreadSet.insert(threadID).second)
 			mutex->waitingThreads.push_back(threadID);
@@ -950,3 +950,3 @@
 			// May be in a tight loop timing out (where we don't remove from waitingThreads yet), don't want to add duplicates.
-			if (std::find(mutex->waitingThreads.begin(), mutex->waitingThreads.end(), threadID) == mutex->waitingThreads.end())
+			if (mutex->waitingThreadSet.insert(threadID).second)
 				mutex->waitingThreads.push_back(threadID);
@@ -985,3 +985,3 @@
 			// May be in a tight loop timing out (where we don't remove from waitingThreads yet), don't want to add duplicates.
-			if (std::find(mutex->waitingThreads.begin(), mutex->waitingThreads.end(), threadID) == mutex->waitingThreads.end())
+			if (mutex->waitingThreadSet.insert(threadID).second)
 				mutex->waitingThreads.push_back(threadID);
#
# CWE-407: sceKernelLockMutex / sceKernelLockMutexCB /
# sceKernelLockLwMutex / sceKernelLockLwMutexCB each scan
# mutex->waitingThreads vector with std::find before push_back —
# O(W) per lock attempt where W = number of waiting threads.
# The code comment says "May be in a tight loop timing out" — that
# tight-loop scenario is exactly where O(W) dedup compounds:
# T attempts * W waiters = O(T*W) total work per timeout cycle.
# Fix: maintain parallel unordered_set<SceUID> waitingThreadSet for
# O(1) dedup; remove from set wherever waitingThreads is cleared/erased.
# Severity: MEDIUM — mutex lock is a hot HLE synchronization path;
# games with thread pools or producer-consumer patterns will trigger
# this on every lock contention timeout cycle.
# Sites: sceKernelLockMutex (line 548), sceKernelLockMutexCB (line 570),
#        sceKernelLockLwMutex (line 951), sceKernelLockLwMutexCB (line 986).