From 52332e8d75800952ac96c2f34c053a921585528d Mon Sep 17 00:00:00 2001
From: Michael Scire <SciresM@gmail.com>
Date: Tue, 19 Oct 2021 02:45:29 -0700
Subject: [PATCH] kern: use 13.0.0 revised KLightLock logic

---
 .../include/mesosphere/kern_k_light_lock.hpp  | 19 +++++++------------
 .../source/kern_k_light_lock.cpp              |  8 +++++---
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/libraries/libmesosphere/include/mesosphere/kern_k_light_lock.hpp b/libraries/libmesosphere/include/mesosphere/kern_k_light_lock.hpp
index 5cd809d4f..36bbd1af8 100644
--- a/libraries/libmesosphere/include/mesosphere/kern_k_light_lock.hpp
+++ b/libraries/libmesosphere/include/mesosphere/kern_k_light_lock.hpp
@@ -37,16 +37,12 @@ namespace ams::kern {
                     uintptr_t old_tag = m_tag.load(std::memory_order_relaxed);
 
                     while (!m_tag.compare_exchange_weak(old_tag, (old_tag == 0) ? cur_thread : old_tag | 1, std::memory_order_acquire)) {
-                        if ((old_tag | 1) == cur_thread_tag) {
-                            return;
-                        }
+                        /* ... */
                     }
 
-                    if ((old_tag == 0) || ((old_tag | 1) == cur_thread_tag)) {
+                    if (old_tag == 0 || this->LockSlowPath(old_tag | 1, cur_thread)) {
                         break;
                     }
-
-                    this->LockSlowPath(old_tag | 1, cur_thread);
                 }
             }
 
@@ -54,15 +50,14 @@ namespace ams::kern {
                 MESOSPHERE_ASSERT_THIS();
 
                 const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer());
+
                 uintptr_t expected = cur_thread;
-                do {
-                    if (expected != cur_thread) {
-                        return this->UnlockSlowPath(cur_thread);
-                    }
-                } while (!m_tag.compare_exchange_weak(expected, 0, std::memory_order_release));
+                if (!m_tag.compare_exchange_strong(expected, 0, std::memory_order_release)) {
+                    this->UnlockSlowPath(cur_thread);
+                }
             }
 
-            void LockSlowPath(uintptr_t owner, uintptr_t cur_thread);
+            bool LockSlowPath(uintptr_t owner, uintptr_t cur_thread);
             void UnlockSlowPath(uintptr_t cur_thread);
 
             ALWAYS_INLINE bool IsLocked() const { return m_tag.load() != 0; }
diff --git a/libraries/libmesosphere/source/kern_k_light_lock.cpp b/libraries/libmesosphere/source/kern_k_light_lock.cpp
index e463bfe9f..f1949ce8d 100644
--- a/libraries/libmesosphere/source/kern_k_light_lock.cpp
+++ b/libraries/libmesosphere/source/kern_k_light_lock.cpp
@@ -31,7 +31,7 @@ namespace ams::kern {
 
     }
 
-    void KLightLock::LockSlowPath(uintptr_t _owner, uintptr_t _cur_thread) {
+    bool KLightLock::LockSlowPath(uintptr_t _owner, uintptr_t _cur_thread) {
         KThread *cur_thread = reinterpret_cast<KThread *>(_cur_thread);
         ThreadQueueImplForKLightLock wait_queue;
 
@@ -40,8 +40,8 @@ namespace ams::kern {
             KScopedSchedulerLock sl;
 
             /* Ensure we actually have locking to do. */
-            if (AMS_UNLIKELY(m_tag.load(std::memory_order_relaxed) != _owner)) {
-                return;
+            if (m_tag.load(std::memory_order_relaxed) != _owner) {
+                return false;
             }
 
             /* Add the current thread as a waiter on the owner. */
@@ -56,6 +56,8 @@ namespace ams::kern {
                 owner_thread->ContinueIfHasKernelWaiters();
             }
         }
+
+        return true;
     }
 
     void KLightLock::UnlockSlowPath(uintptr_t _cur_thread) {