Kernel/Tasks: Allow Kernel processes to be shut down

Since we never check a kernel process's state like a userland process,
it's possible for a kernel process to ignore the fact that someone is
trying to kill it, and continue running. This is not desireable if we
want to properly shutdown all processes, including Kernel ones.

Kernel/Bus/USB/UHCI/UHCIController.cpp

@@ -586,12 +586,14 @@ size_t UHCIController::poll_transfer_queue(QueueHead& transfer_queue)
 ErrorOr<void> UHCIController::spawn_port_process()
 {
     TRY(Process::create_kernel_process(TRY(KString::try_create("UHCI Hot Plug Task"sv)), [&] {
-        for (;;) {
+        while (!Process::current().is_dying()) {
             if (m_root_hub)
                 m_root_hub->check_for_port_updates();
 
             (void)Thread::current()->sleep(Duration::from_seconds(1));
         }
+        Process::current().sys$exit(0);
+        VERIFY_NOT_REACHED();
     }));
     return {};
 }
@@ -600,7 +602,7 @@ ErrorOr<void> UHCIController::spawn_async_poll_process()
 {
     TRY(Process::create_kernel_process(TRY(KString::try_create("UHCI Async Poll Task"sv)), [&] {
         u16 poll_interval_ms = 1024;
-        for (;;) {
+        while (!Process::current().is_dying()) {
             {
                 SpinlockLocker locker { m_async_lock };
                 for (OwnPtr<AsyncTransferHandle>& handle : m_active_async_transfers) {
@@ -618,6 +620,8 @@ ErrorOr<void> UHCIController::spawn_async_poll_process()
             }
             (void)Thread::current()->sleep(Duration::from_milliseconds(poll_interval_ms));
         }
+        Process::current().sys$exit(0);
+        VERIFY_NOT_REACHED();
     }));
     return {};
 }

Kernel/FileSystem/Plan9FS/FileSystem.cpp

@@ -327,7 +327,7 @@ size_t Plan9FS::adjust_buffer_size(size_t size) const
 void Plan9FS::thread_main()
 {
     dbgln("Plan9FS: Thread running");
-    do {
+    while (!Process::current().is_dying()) {
         auto result = read_and_dispatch_one_message();
         if (result.is_error()) {
             // If we fail to read, wake up everyone with an error.
@@ -342,7 +342,7 @@ void Plan9FS::thread_main()
             dbgln("Plan9FS: Thread terminating, error reading");
             return;
         }
-    } while (!m_thread_shutdown);
+    }
     dbgln("Plan9FS: Thread terminating");
 }
 
@@ -356,6 +356,8 @@ void Plan9FS::ensure_thread()
         auto [_, thread] = Process::create_kernel_process(process_name.release_value(), [&]() {
             thread_main();
             m_thread_running.store(false, AK::MemoryOrder::memory_order_release);
+            Process::current().sys$exit(0);
+            VERIFY_NOT_REACHED();
         }).release_value_but_fixme_should_propagate_errors();
         m_thread = move(thread);
     }

Kernel/FileSystem/Plan9FS/FileSystem.h

@@ -139,7 +139,6 @@ private:
     Spinlock<LockRank::None> m_thread_lock {};
     RefPtr<Thread> m_thread;
     Atomic<bool> m_thread_running { false };
-    Atomic<bool, AK::MemoryOrder::memory_order_relaxed> m_thread_shutdown { false };
 };
 
 }

Kernel/Net/NetworkTask.cpp

@@ -96,7 +96,7 @@ void NetworkTask_main(void*)
     auto buffer = (u8*)buffer_region->vaddr().get();
     UnixDateTime packet_timestamp;
 
-    for (;;) {
+    while (!Process::current().is_dying()) {
         flush_delayed_tcp_acks();
         retransmit_tcp_packets();
         size_t packet_size = dequeue_packet(buffer, buffer_size, packet_timestamp);
@@ -127,6 +127,8 @@ void NetworkTask_main(void*)
             dbgln_if(ETHERNET_DEBUG, "NetworkTask: Unknown ethernet type {:#04x}", eth.ether_type());
         }
     }
+    Process::current().sys$exit(0);
+    VERIFY_NOT_REACHED();
 }
 
 void handle_arp(EthernetFrameHeader const& eth, size_t frame_size)

Kernel/Tasks/FinalizerTask.cpp

@@ -16,7 +16,7 @@ static constexpr StringView finalizer_task_name = "Finalizer Task"sv;
 static void finalizer_task(void*)
 {
     Thread::current()->set_priority(THREAD_PRIORITY_LOW);
-    for (;;) {
+    while (!Process::current().is_dying()) {
         // The order of this if-else is important: We want to continue trying to finalize the threads in case
         // Thread::finalize_dying_threads set g_finalizer_has_work back to true due to OOM conditions
         if (g_finalizer_has_work.exchange(false, AK::MemoryOrder::memory_order_acq_rel) == true)
@@ -24,6 +24,8 @@ static void finalizer_task(void*)
         else
             g_finalizer_wait_queue->wait_forever(finalizer_task_name);
     }
+    Process::current().sys$exit(0);
+    VERIFY_NOT_REACHED();
 }
 
 UNMAP_AFTER_INIT void FinalizerTask::spawn()

Kernel/Tasks/SyncTask.cpp

@@ -16,10 +16,12 @@ UNMAP_AFTER_INIT void SyncTask::spawn()
 {
     MUST(Process::create_kernel_process(KString::must_create("VFS Sync Task"sv), [] {
         dbgln("VFS SyncTask is running");
-        for (;;) {
+        while (!Process::current().is_dying()) {
             VirtualFileSystem::sync();
             (void)Thread::current()->sleep(Duration::from_seconds(1));
         }
+        Process::current().sys$exit(0);
+        VERIFY_NOT_REACHED();
     }));
 }
 

Kernel/Tasks/WorkQueue.cpp

@@ -28,7 +28,7 @@ UNMAP_AFTER_INIT WorkQueue::WorkQueue(StringView name)
     if (name_kstring.is_error())
         TODO();
     auto [_, thread] = Process::create_kernel_process(name_kstring.release_value(), [this] {
-        for (;;) {
+        while (!Process::current().is_dying()) {
             WorkItem* item;
             bool have_more;
             m_items.with([&](auto& items) {
@@ -44,6 +44,8 @@ UNMAP_AFTER_INIT WorkQueue::WorkQueue(StringView name)
             }
             [[maybe_unused]] auto result = m_wait_queue.wait_on({});
         }
+        Process::current().sys$exit(0);
+        VERIFY_NOT_REACHED();
     }).release_value_but_fixme_should_propagate_errors();
     m_thread = move(thread);
 }