Add an undertaker task that is responsible for destroying dead tasks.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/d90d125dfe1

Kernel/Task.cpp

@@ -17,6 +17,7 @@ Task* s_kernelTask;
 
 static pid_t next_pid;
 static InlineLinkedList<Task>* s_tasks;
+static InlineLinkedList<Task>* s_deadTasks;
 
 static bool contextSwitch(Task*);
 
@@ -52,6 +53,7 @@ void Task::initialize()
     current = nullptr;
     next_pid = 0;
     s_tasks = new InlineLinkedList<Task>;
+    s_deadTasks = new InlineLinkedList<Task>;
     s_kernelTask = new Task(0, "colonel", IPC::Handle::Any, Task::Ring0);
     redoKernelTaskTSS();
     loadTaskRegister(s_kernelTask->selector());
@@ -213,7 +215,6 @@ Task::Task(String&& name, uid_t uid, gid_t gid)
     m_tss.esp = m_stackTop;
 
     // Set up a separate stack for Ring0.
-    // FIXME: Don't leak this stack.
     m_kernelStack = kmalloc(defaultStackSize);
     DWORD ring0StackTop = ((DWORD)m_kernelStack + defaultStackSize) & 0xffffff8;
     m_tss.ss0 = 0x10;
@@ -336,14 +337,10 @@ Task::~Task()
     delete [] m_ldtEntries;
     m_ldtEntries = nullptr;
 
-    // FIXME: The task's kernel stack is currently leaked, because otherwise we GPF.
-    //        This obviously needs figuring out.
-#if 0
     if (m_kernelStack) {
         kfree(m_kernelStack);
         m_kernelStack = nullptr;
     }
-#endif
 }
 
 void Task::dumpRegions()
@@ -375,7 +372,7 @@ void Task::sys$exit(int status)
         HANG;
     }
 
-    delete this;
+    s_deadTasks->append(this);
 
     switchNow();
 }
@@ -395,11 +392,21 @@ void Task::taskDidCrash(Task* crashedTask)
         HANG;
     }
 
-    delete crashedTask;
+    s_deadTasks->append(crashedTask);
 
     switchNow();
 }
 
+void Task::doHouseKeeping()
+{
+    Task* next = nullptr;
+    for (auto* deadTask = s_deadTasks->head(); deadTask; deadTask = next) {
+        next = deadTask->next();
+        delete deadTask;
+    }
+    s_deadTasks->clear();
+}
+
 void yield()
 {
     if (!current) {

Kernel/Task.h

@@ -67,6 +67,8 @@ public:
 
     FileHandle* fileHandleIfExists(int fd);
 
+    static void doHouseKeeping();
+
     bool acceptsMessageFrom(Task&);
 
     void block(Task::State);

Kernel/init.cpp

@@ -28,6 +28,7 @@
 #include "ProcFileSystem.h"
 
 #define TEST_VFS
+//#define STRESS_TEST_SPAWNING
 //#define TEST_ELF_LOADER
 //#define TEST_CRASHY_USER_PROCESSES
 
@@ -95,6 +96,15 @@ void banner()
     kprintf("\n");
 }
 
+static void undertaker_main() NORETURN;
+static void undertaker_main()
+{
+    for (;;) {
+        Task::doHouseKeeping();
+        sleep(10);
+    }
+}
+
 static void init_stage2() NORETURN;
 static void init_stage2()
 {
@@ -105,7 +115,7 @@ static void init_stage2()
     auto keyboard = make<Keyboard>();
 
     extern void panel_main();
-    new Task(panel_main, "panel", IPC::Handle::PanelTask, Task::Ring0);
+    //new Task(panel_main, "panel", IPC::Handle::PanelTask, Task::Ring0);
     //new Task(led_disco, "led-disco", IPC::Handle::Any, Task::Ring0);
 
     Disk::initialize();
@@ -171,6 +181,19 @@ static void init_stage2()
     }
 #endif
 
+#ifdef STRESS_TEST_SPAWNING
+    dword lastAlloc = sum_alloc;
+
+    for (unsigned i = 0; i < 100; ++i) {
+        auto* shTask = Task::create("/bin/id", (uid_t)100, (gid_t)100);
+        kprintf("malloc stats: alloc:%u free:%u\n", sum_alloc, sum_free);
+        kprintf("sizeof(Task):%u\n", sizeof(Task));
+        kprintf("delta:%u\n",sum_alloc - lastAlloc);
+        lastAlloc = sum_alloc;
+        sleep(600);
+    }
+#endif
+
     auto* shTask = Task::create("/bin/sh", (uid_t)100, (gid_t)100);
 
     //new Task(motd_main, "motd", IPC::Handle::MotdTask, Task::Ring0);
@@ -221,6 +244,8 @@ void init()
 
     Task::initialize();
 
+    new Task(undertaker_main, "undertaker", IPC::Handle::UserTask, Task::Ring0);
+
     auto* init2 = new Task(init_stage2, "init", IPC::Handle::InitTask, Task::Ring0);
     scheduleNewTask();