Ensure thread doesn't migrate during InsertThread

As we didn't hold `coreMigrationMutex`, the thread could simply migrate during `InsertThread` which would lead to the thread potentially never waking up as it's been inserted on a non-resident core.

Co-authored-by: PixelyIon <pixelyion@protonmail.com>

app/src/main/cpp/skyline/kernel/scheduler.cpp

@@ -86,8 +86,9 @@ namespace skyline::kernel {
     }
 
     void Scheduler::InsertThread(const std::shared_ptr<type::KThread> &thread) {
+        std::scoped_lock migrationLock{thread->coreMigrationMutex};
         auto &core{cores.at(thread->coreId)};
-        std::unique_lock lock(core.mutex);
+        std::unique_lock lock{core.mutex};
 
         if (thread->isPaused) {
             // We cannot insert a thread that is paused, so we need to wait until it has been resumed

app/src/main/cpp/skyline/kernel/scheduler.h

@@ -58,7 +58,7 @@ namespace skyline {
             std::list<std::shared_ptr<type::KThread>> parkedQueue; //!< A queue of threads which are parked and waiting on core migration
 
             /**
-             * @brief Migrate a thread from its resident core to its ideal core
+             * @brief Migrate a thread from its resident core to the target core
              * @note 'KThread::coreMigrationMutex' **must** be locked by the calling thread prior to calling this
              * @note This is used to handle non-cooperative core affinity mask changes where the resident core is not in its new affinity mask
              */

app/src/main/cpp/skyline/kernel/types/KThread.h

@@ -50,7 +50,7 @@ namespace skyline {
             std::atomic<i8> basePriority; //!< The priority of the thread for the scheduler without any priority-inheritance
             std::atomic<i8> priority; //!< The priority of the thread for the scheduler including priority-inheritance
 
-            std::mutex coreMigrationMutex; //!< Synchronizes operations which depend on which core the thread is running on
+            std::recursive_mutex coreMigrationMutex; //!< Synchronizes operations which depend on which core the thread is running on
             u8 idealCore; //!< The ideal CPU core for this thread to run on
             u8 coreId; //!< The CPU core on which this thread is running
             CoreMask affinityMask{}; //!< A mask of CPU cores this thread is allowed to run on