Kernel: Fix thread joining issues

The thread joining logic hadn't been updated to account for the subtle
differences introduced by software context switching. This fixes several
race conditions related to thread destruction and joining, as well as
finalization which did not properly account for detached state and the
fact that threads can be joined after termination as long as they're not
detached.

Fixes #3596

1 files changed, 12 insertions, 22 deletions

diff --git a/Kernel/Syscalls/thread.cpp b/Kernel/Syscalls/thread.cpp
index e718539cb4..bd957da5df 100644
--- a/Kernel/Syscalls/thread.cpp
+++ b/Kernel/Syscalls/thread.cpp
@@ -71,7 +71,8 @@ int Process::sys$create_thread(void* (*entry)(void*), Userspace<const Syscall::S
     thread->set_name(builder.to_string());
 
     thread->set_priority(requested_thread_priority);
-    thread->set_joinable(is_thread_joinable);
+    if (!is_thread_joinable)
+        thread->detach();
 
     auto& tss = thread->tss();
     tss.eip = (FlatPtr)entry;
@@ -109,7 +110,7 @@ int Process::sys$detach_thread(pid_t tid)
     if (!thread->is_joinable())
         return -EINVAL;
 
-    thread->set_joinable(false);
+    thread->detach();
     return 0;
 }
 
@@ -126,31 +127,20 @@ int Process::sys$join_thread(pid_t tid, Userspace<void**> exit_value)
     if (thread == current_thread)
         return -EDEADLK;
 
-    if (thread->m_joinee == current_thread)
-        return -EDEADLK;
-
-    ASSERT(thread->m_joiner != current_thread);
-    if (thread->m_joiner)
-        return -EINVAL;
-
-    if (!thread->is_joinable())
-        return -EINVAL;
-
     void* joinee_exit_value = nullptr;
 
     // NOTE: pthread_join() cannot be interrupted by signals. Only by death.
     for (;;) {
-        auto result = current_thread->block<Thread::JoinBlocker>(nullptr, *thread, joinee_exit_value);
+        KResult try_join_result(KSuccess);
+        auto result = current_thread->block<Thread::JoinBlocker>(nullptr, *thread, try_join_result, joinee_exit_value);
+        if (result == Thread::BlockResult::NotBlocked) {
+            ASSERT_INTERRUPTS_DISABLED();
+            if (try_join_result.is_error())
+                return try_join_result.error();
+            break;
+        }
         if (result == Thread::BlockResult::InterruptedByDeath) {
-            // NOTE: This cleans things up so that Thread::finalize() won't
-            //       get confused about a missing joiner when finalizing the joinee.
-            InterruptDisabler disabler_t;
-
-            if (current_thread->m_joinee) {
-                current_thread->m_joinee->m_joiner = nullptr;
-                current_thread->m_joinee = nullptr;
-            }
-
+            ASSERT_INTERRUPTS_DISABLED();
             break;
         }
     }