kernel: Leave reaping to the reap thread

This seems to fix previous problems. Apparently reaping a thread somewhat corrupts/replaces the calling thread's address space.

I should've known there's a reason we do it in a separate kernel thread...

kernel/src/main.cpp

@@ -26,9 +26,11 @@ void reap_thread()
     {
         CPU::disable_interrupts();
         auto dying_threads = Scheduler::check_for_dying_threads();
+        auto dead_processes = Scheduler::check_for_dead_processes();
         CPU::enable_interrupts();
 
         dying_threads.consume([](Thread* thread) { Scheduler::reap_thread(thread); });
+        dead_processes.consume([](Process* p) { Scheduler::reap_process(p); });
 
         kernel_wait_for_event();
     }

kernel/src/sys/exec.cpp

@@ -113,6 +113,7 @@ Result<u64> sys_execve(Registers* regs, SyscallArgs args)
         if (t != thread) t->quit();
         return true;
     });
+    Scheduler::signal_reap_thread();
 
     current->thread_count = 1;
 
@@ -145,6 +146,7 @@ Result<u64> sys_execve(Registers* regs, SyscallArgs args)
     }
 
     current->cmdline = cmdline.chars();
+    thread->cmdline = cmdline.chars();
 
     image->apply(thread);
 

kernel/src/sys/waitpid.cpp

@@ -25,8 +25,8 @@ Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
         if (options & WNOHANG) return err(EAGAIN);
 
     wait_for_child:
-        if (target->alive()) kernel_wait(pid);
-        if (current->interrupted)
+        if (!target->dead()) kernel_wait(pid);
+        if (current->interrupted && current->pending_signal() != SIGCHLD)
         {
             kdbgln("signal: waitpid interrupted by signal");
             if (current->will_ignore_pending_signal())
@@ -37,7 +37,7 @@ Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
             return err(EINTR);
         }
 
-        check(!target->alive());
+        check(target->dead());
     }
     else if (pid == -1)
     {
@@ -50,7 +50,7 @@ Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
 
         wait_for_any_child:
             kernel_wait(pid);
-            if (current->interrupted)
+            if (current->interrupted && current->pending_signal() != SIGCHLD)
             {
                 kdbgln("signal: waitpid interrupted by signal");
                 if (current->will_ignore_pending_signal())
@@ -64,7 +64,7 @@ Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
             check(current->child_being_waited_for != -1);
 
             target = TRY(Result<Process*>::from_option(Scheduler::find_by_pid(current->child_being_waited_for), ESRCH));
-            check(!target->alive());
+            check(!target->dead());
         }
         else
             target = child.value();
@@ -80,7 +80,8 @@ Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
     current->process->user_ticks_children += target->user_ticks_self + target->user_ticks_children;
     current->process->kernel_ticks_children += target->kernel_ticks_self + target->kernel_ticks_children;
 
-    Scheduler::reap_process(target);
+    target->thread_count = PROCESS_SHOULD_REAP;
+    Scheduler::signal_reap_thread();
 
     if (status_ptr)
         if (!MemoryManager::copy_to_user_typed(status_ptr, &status)) return err(EFAULT);

kernel/src/thread/Scheduler.cpp

@@ -117,6 +117,7 @@ namespace Scheduler
         process->thread_count = 1;
         process->virtual_clock.set_resolution(1'000'000);
         process->profiling_clock.set_resolution(1'000'000);
+        process->cmdline = name;
         process->is_kernel = true;
 
         g_threads.append(thread);
@@ -172,6 +173,7 @@ namespace Scheduler
         process->id = 1;
         process->pgid = 1;
         process->thread_count = 1;
+        process->cmdline = name;
 
         Vector<String> args;
         auto name_string = TRY(String::from_cstring(name));
@@ -228,6 +230,8 @@ namespace Scheduler
 
     void reap_process(Process* process)
     {
+        CPU::disable_interrupts();
+
         // FIXME: Shouldn't all this be done when the timers' destructors are called?
         process->real_timer.disarm();
         process->virtual_timer.disarm();
@@ -238,6 +242,8 @@ namespace Scheduler
         }
 
         delete process;
+
+        CPU::enable_interrupts();
     }
 
     void reap_thread(Thread* thread)
@@ -378,6 +384,21 @@ namespace Scheduler
         return result;
     }
 
+    LinkedList<Process> check_for_dead_processes()
+    {
+        LinkedList<Process> result;
+
+        g_processes.delayed_for_each([&](Process* p) {
+            if (p->thread_count == PROCESS_SHOULD_REAP)
+            {
+                g_processes.remove(p);
+                result.append(p);
+            }
+        });
+
+        return result;
+    }
+
     Option<Process*> find_by_pid(pid_t pid)
     {
         for (auto* const process : g_processes)
@@ -405,7 +426,7 @@ namespace Scheduler
         Option<Process*> result;
 
         for_each_child(process, [&](Process* child) {
-            if (!result.has_value() && !child->alive())
+            if (!result.has_value() && child->dead())
             {
                 result = child;
                 return false;
@@ -469,6 +490,7 @@ void kernel_wait_for_event()
 [[noreturn]] void kernel_exit()
 {
     g_current->state = ThreadState::Dying;
+    g_current->process->thread_count = PROCESS_SHOULD_REAP;
     Scheduler::signal_reap_thread();
     kernel_yield();
     unreachable();

kernel/src/thread/Scheduler.h

@@ -35,6 +35,7 @@ namespace Scheduler
     void invoke(Registers* regs);
 
     LinkedList<Thread> check_for_dying_threads();
+    LinkedList<Process> check_for_dead_processes();
 
     Option<Process*> find_by_pid(pid_t pid);
 

kernel/src/thread/Thread.cpp

@@ -137,6 +137,7 @@ Result<SharedPtr<VFS::Inode>> Process::resolve_atfile(int dirfd, const String& p
         thread->quit();
         return true;
     });
+    Scheduler::signal_reap_thread();
 
     thread_count = 0;
 
@@ -276,6 +277,15 @@ void Thread::process_pending_signals(Registers* current_regs)
     }
 }
 
+int Thread::pending_signal()
+{
+    for (int i = 0; i < NSIG; i++)
+    {
+        if (pending_signals.get(i)) { return i + 1; }
+    }
+    return 0;
+}
+
 bool Thread::will_ignore_pending_signal()
 {
     for (int i = 0; i < NSIG; i++)

kernel/src/thread/Thread.h

@@ -20,6 +20,7 @@
 #endif
 
 constexpr int MAX_POSIX_TIMERS = 64;
+constexpr i64 PROCESS_SHOULD_REAP = -1;
 
 class Timer;
 
@@ -49,7 +50,7 @@ struct Credentials
 
 struct Process : public LinkedListNode<Process>
 {
-    Atomic<usize> thread_count;
+    Atomic<i64> thread_count;
 
     pid_t id;
     Atomic<pid_t> pgid { 0 };
@@ -122,6 +123,11 @@ struct Process : public LinkedListNode<Process>
         return thread_count > 0;
     }
 
+    bool dead()
+    {
+        return thread_count == 0;
+    }
+
     static Process* current();
 
     [[noreturn]] void exit(int status);
@@ -202,6 +208,7 @@ struct Thread : public LinkedListNode<Thread>
 
     void process_pending_signals(Registers* current_regs);
 
+    int pending_signal();
     bool will_ignore_pending_signal();
 
     bool deliver_signal(int signo, Registers* current_regs);