Kernel: Make Threads always have a name

We previously allowed Thread to exist in a state where its m_name was
null, and had to work around that in various places.

This patch removes that possibility and forces those who would create a
thread (or change the name of one) to provide a NonnullOwnPtr<KString>
with the name.

Kernel/Process.cpp

@@ -739,7 +739,7 @@ KResult Process::send_signal(u8 signal, Process* sender)
     return ESRCH;
 }
 
-RefPtr<Thread> Process::create_kernel_thread(void (*entry)(void*), void* entry_data, u32 priority, OwnPtr<KString> name, u32 affinity, bool joinable)
+RefPtr<Thread> Process::create_kernel_thread(void (*entry)(void*), void* entry_data, u32 priority, NonnullOwnPtr<KString> name, u32 affinity, bool joinable)
 {
     VERIFY((priority >= THREAD_PRIORITY_MIN) && (priority <= THREAD_PRIORITY_MAX));
 

Kernel/Process.h

@@ -187,7 +187,7 @@ public:
 
     static NonnullRefPtrVector<Process> all_processes();
 
-    RefPtr<Thread> create_kernel_thread(void (*entry)(void*), void* entry_data, u32 priority, OwnPtr<KString> name, u32 affinity = THREAD_AFFINITY_DEFAULT, bool joinable = true);
+    RefPtr<Thread> create_kernel_thread(void (*entry)(void*), void* entry_data, u32 priority, NonnullOwnPtr<KString> name, u32 affinity = THREAD_AFFINITY_DEFAULT, bool joinable = true);
 
     bool is_profiling() const { return m_profiling; }
     void set_profiling(bool profiling) { m_profiling = profiling; }

Kernel/Scheduler.cpp

@@ -417,7 +417,7 @@ UNMAP_AFTER_INIT void Scheduler::initialize()
     VERIFY(s_colonel_process);
     VERIFY(idle_thread);
     idle_thread->set_priority(THREAD_PRIORITY_MIN);
-    idle_thread->set_name(KString::try_create("idle thread #0"));
+    idle_thread->set_name(KString::must_create("idle thread #0"));
 
     set_idle_thread(idle_thread);
 }
@@ -436,7 +436,7 @@ UNMAP_AFTER_INIT Thread* Scheduler::create_ap_idle_thread(u32 cpu)
     VERIFY(Processor::is_bootstrap_processor());
 
     VERIFY(s_colonel_process);
-    Thread* idle_thread = s_colonel_process->create_kernel_thread(idle_loop, nullptr, THREAD_PRIORITY_MIN, KString::try_create(String::formatted("idle thread #{}", cpu)), 1 << cpu, false);
+    Thread* idle_thread = s_colonel_process->create_kernel_thread(idle_loop, nullptr, THREAD_PRIORITY_MIN, KString::must_create(String::formatted("idle thread #{}", cpu)), 1 << cpu, false);
     VERIFY(idle_thread);
     return idle_thread;
 }

Kernel/Syscalls/execve.cpp

@@ -498,6 +498,11 @@ KResult Process::do_exec(NonnullRefPtr<FileDescription> main_program_description
     if (parts.is_empty())
         return ENOENT;
 
+    auto new_process_name = parts.take_last();
+    auto new_main_thread_name = KString::try_create(new_process_name);
+    if (!new_main_thread_name)
+        return ENOMEM;
+
     auto main_program_metadata = main_program_description->metadata();
 
     auto load_result = TRY(load(main_program_description, interpreter_description, main_program_header));
@@ -620,8 +625,8 @@ KResult Process::do_exec(NonnullRefPtr<FileDescription> main_program_description
 
     // NOTE: Be careful to not trigger any page faults below!
 
-    m_name = parts.take_last();
+    m_name = move(new_process_name);
-    new_main_thread->set_name(KString::try_create(m_name));
+    new_main_thread->set_name(new_main_thread_name.release_nonnull());
 
     {
         ProtectedDataMutationScope scope { *this };

Kernel/Syscalls/thread.cpp

@@ -43,11 +43,16 @@ KResultOr<FlatPtr> Process::sys$create_thread(void* (*entry)(void*), Userspace<c
 
     auto thread = TRY(Thread::try_create(*this));
 
+    // FIXME: Don't make a temporary String here
+    auto new_thread_name = KString::try_create(String::formatted("{} [{}]", m_name, thread->tid().value()));
+    if (!new_thread_name)
+        return ENOMEM;
+
     // We know this thread is not the main_thread,
     // So give it a unique name until the user calls $set_thread_name on it
     // length + 4 to give space for our extra junk at the end
     StringBuilder builder(m_name.length() + 4);
-    thread->set_name(KString::try_create(String::formatted("{} [{}]", m_name, thread->tid().value())));
+    thread->set_name(new_thread_name.release_nonnull());
 
     if (!is_thread_joinable)
         thread->detach();

Kernel/Thread.cpp

@@ -47,11 +47,13 @@ KResultOr<NonnullRefPtr<Thread>> Thread::try_create(NonnullRefPtr<Process> proce
         return ENOMEM;
 
     auto name = KString::try_create(process->name());
+    if (!name)
+        return ENOMEM;
 
-    return adopt_nonnull_ref_or_enomem(new (nothrow) Thread(move(process), move(kernel_stack_region), block_timer.release_nonnull(), move(name)));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) Thread(move(process), move(kernel_stack_region), block_timer.release_nonnull(), name.release_nonnull()));
 }
 
-Thread::Thread(NonnullRefPtr<Process> process, NonnullOwnPtr<Memory::Region> kernel_stack_region, NonnullRefPtr<Timer> block_timer, OwnPtr<KString> name)
+Thread::Thread(NonnullRefPtr<Process> process, NonnullOwnPtr<Memory::Region> kernel_stack_region, NonnullRefPtr<Timer> block_timer, NonnullOwnPtr<KString> name)
     : m_process(move(process))
     , m_kernel_stack_region(move(kernel_stack_region))
     , m_name(move(name))

Kernel/Thread.h

@@ -194,10 +194,10 @@ public:
     {
         // NOTE: Whoever is calling this needs to be holding our lock while reading the name.
         VERIFY(m_lock.is_locked_by_current_processor());
-        return m_name ? m_name->view() : StringView {};
+        return m_name->view();
     }
 
-    void set_name(OwnPtr<KString> name)
+    void set_name(NonnullOwnPtr<KString> name)
     {
         SpinlockLocker lock(m_lock);
         m_name = move(name);
@@ -1202,7 +1202,7 @@ public:
     String backtrace();
 
 private:
-    Thread(NonnullRefPtr<Process>, NonnullOwnPtr<Memory::Region>, NonnullRefPtr<Timer>, OwnPtr<KString>);
+    Thread(NonnullRefPtr<Process>, NonnullOwnPtr<Memory::Region>, NonnullRefPtr<Timer>, NonnullOwnPtr<KString>);
 
     IntrusiveListNode<Thread> m_process_thread_list_node;
     int m_runnable_priority { -1 };
@@ -1333,7 +1333,7 @@ private:
 
     FPUState m_fpu_state {};
     State m_state { Invalid };
-    OwnPtr<KString> m_name;
+    NonnullOwnPtr<KString> m_name;
     u32 m_priority { THREAD_PRIORITY_NORMAL };
 
     State m_stop_state { Invalid };