ladybird/Kernel/Process.cpp

/*
 * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Singleton.h>
#include <AK/StdLibExtras.h>
#include <AK/Time.h>
#include <AK/Types.h>
#include <Kernel/API/Syscall.h>
#include <Kernel/Arch/InterruptDisabler.h>
#include <Kernel/Coredump.h>
#include <Kernel/Credentials.h>
#include <Kernel/Debug.h>
#include <Kernel/Devices/DeviceManagement.h>
#ifdef ENABLE_KERNEL_COVERAGE_COLLECTION
#    include <Kernel/Devices/KCOVDevice.h>
#endif
#include <Kernel/API/POSIX/errno.h>
#include <Kernel/Devices/NullDevice.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/OpenFileDescription.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
#include <Kernel/KBufferBuilder.h>
#include <Kernel/KSyms.h>
#include <Kernel/Memory/AnonymousVMObject.h>
#include <Kernel/Memory/PageDirectory.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Panic.h>
#include <Kernel/PerformanceEventBuffer.h>
#include <Kernel/PerformanceManager.h>
#include <Kernel/Process.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Sections.h>
#include <Kernel/StdLib.h>
#include <Kernel/TTY/TTY.h>
#include <Kernel/Thread.h>
#include <Kernel/ThreadTracer.h>
#include <Kernel/TimerQueue.h>
#include <LibC/limits.h>

namespace Kernel {

static void create_signal_trampoline();

extern ProcessID g_init_pid;

RecursiveSpinlock g_profiling_lock { LockRank::None };
static Atomic<pid_t> next_pid;
static Singleton<SpinlockProtected<Process::List>> s_all_instances;
READONLY_AFTER_INIT Memory::Region* g_signal_trampoline_region;

static Singleton<MutexProtected<OwnPtr<KString>>> s_hostname;

MutexProtected<OwnPtr<KString>>& hostname()
{
    return *s_hostname;
}

SpinlockProtected<Process::List>& Process::all_instances()
{
    return *s_all_instances;
}

ProcessID Process::allocate_pid()
{
    // Overflow is UB, and negative PIDs wreck havoc.
    // TODO: Handle PID overflow
    // For example: Use an Atomic<u32>, mask the most significant bit,
    // retry if PID is already taken as a PID, taken as a TID,
    // takes as a PGID, taken as a SID, or zero.
    return next_pid.fetch_add(1, AK::MemoryOrder::memory_order_acq_rel);
}

UNMAP_AFTER_INIT void Process::initialize()
{
    next_pid.store(0, AK::MemoryOrder::memory_order_release);

    // Note: This is called before scheduling is initialized, and before APs are booted.
    //       So we can "safely" bypass the lock here.
    reinterpret_cast<OwnPtr<KString>&>(hostname()) = KString::must_create("courage"sv);

    create_signal_trampoline();
}

void Process::kill_threads_except_self()
{
    InterruptDisabler disabler;

    if (thread_count() <= 1)
        return;

    auto* current_thread = Thread::current();
    for_each_thread([&](Thread& thread) {
        if (&thread == current_thread)
            return;

        if (auto state = thread.state(); state == Thread::State::Dead
            || state == Thread::State::Dying)
            return;

        // We need to detach this thread in case it hasn't been joined
        thread.detach();
        thread.set_should_die();
    });

    u32 dropped_lock_count = 0;
    if (big_lock().force_unlock_exclusive_if_locked(dropped_lock_count) != LockMode::Unlocked)
        dbgln("Process {} big lock had {} locks", *this, dropped_lock_count);
}

void Process::kill_all_threads()
{
    for_each_thread([&](Thread& thread) {
        // We need to detach this thread in case it hasn't been joined
        thread.detach();
        thread.set_should_die();
    });
}

void Process::register_new(Process& process)
{
    // Note: this is essentially the same like process->ref()
    LockRefPtr<Process> new_process = process;
    all_instances().with([&](auto& list) {
        list.prepend(process);
    });
}

ErrorOr<NonnullLockRefPtr<Process>> Process::try_create_user_process(LockRefPtr<Thread>& first_thread, StringView path, UserID uid, GroupID gid, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment, TTY* tty)
{
    auto parts = path.split_view('/');
    if (arguments.is_empty()) {
        auto last_part = TRY(KString::try_create(parts.last()));
        TRY(arguments.try_append(move(last_part)));
    }

    auto path_string = TRY(KString::try_create(path));
    auto name = TRY(KString::try_create(parts.last()));
    auto process = TRY(Process::try_create(first_thread, move(name), uid, gid, ProcessID(0), false, VirtualFileSystem::the().root_custody(), nullptr, tty));

    TRY(process->m_fds.with_exclusive([&](auto& fds) -> ErrorOr<void> {
        TRY(fds.try_resize(Process::OpenFileDescriptions::max_open()));

        auto& device_to_use_as_tty = tty ? (CharacterDevice&)*tty : DeviceManagement::the().null_device();
        auto description = TRY(device_to_use_as_tty.open(O_RDWR));
        auto setup_description = [&](int fd) {
            fds.m_fds_metadatas[fd].allocate();
            fds[fd].set(*description);
        };
        setup_description(0);
        setup_description(1);
        setup_description(2);

        return {};
    }));

    Thread* new_main_thread = nullptr;
    u32 prev_flags = 0;
    if (auto result = process->exec(move(path_string), move(arguments), move(environment), new_main_thread, prev_flags); result.is_error()) {
        dbgln("Failed to exec {}: {}", path, result.error());
        first_thread = nullptr;
        return result.release_error();
    }

    register_new(*process);

    // NOTE: All user processes have a leaked ref on them. It's balanced by Thread::WaitBlockerSet::finalize().
    process->ref();

    {
        SpinlockLocker lock(g_scheduler_lock);
        new_main_thread->set_state(Thread::State::Runnable);
    }

    return process;
}

LockRefPtr<Process> Process::create_kernel_process(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, void (*entry)(void*), void* entry_data, u32 affinity, RegisterProcess do_register)
{
    auto process_or_error = Process::try_create(first_thread, move(name), UserID(0), GroupID(0), ProcessID(0), true);
    if (process_or_error.is_error())
        return {};
    auto process = process_or_error.release_value();

    first_thread->regs().set_ip((FlatPtr)entry);
#if ARCH(I386)
    first_thread->regs().esp = FlatPtr(entry_data); // entry function argument is expected to be in regs.esp
#elif ARCH(X86_64)
    first_thread->regs().rdi = FlatPtr(entry_data); // entry function argument is expected to be in regs.rdi
#else
#    error Unknown architecture
#endif

    if (do_register == RegisterProcess::Yes)
        register_new(*process);

    SpinlockLocker lock(g_scheduler_lock);
    first_thread->set_affinity(affinity);
    first_thread->set_state(Thread::State::Runnable);
    return process;
}

void Process::protect_data()
{
    m_protected_data_refs.unref([&]() {
        MM.set_page_writable_direct(VirtualAddress { &this->m_protected_values_do_not_access_directly }, false);
    });
}

void Process::unprotect_data()
{
    m_protected_data_refs.ref([&]() {
        MM.set_page_writable_direct(VirtualAddress { &this->m_protected_values_do_not_access_directly }, true);
    });
}

ErrorOr<NonnullLockRefPtr<Process>> Process::try_create(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, UserID uid, GroupID gid, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, Process* fork_parent)
{
    OwnPtr<Memory::AddressSpace> new_address_space;
    if (fork_parent) {
        TRY(fork_parent->address_space().with([&](auto& parent_address_space) -> ErrorOr<void> {
            new_address_space = TRY(Memory::AddressSpace::try_create(parent_address_space.ptr()));
            return {};
        }));
    } else {
        new_address_space = TRY(Memory::AddressSpace::try_create(nullptr));
    }
    auto unveil_tree = UnveilNode { TRY(KString::try_create("/"sv)), UnveilMetadata(TRY(KString::try_create("/"sv))) };
    auto credentials = TRY(Credentials::create(uid, gid, uid, gid, uid, gid, {}));
    auto process = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) Process(move(name), move(credentials), ppid, is_kernel_process, move(current_directory), move(executable), tty, move(unveil_tree))));
    TRY(process->attach_resources(new_address_space.release_nonnull(), first_thread, fork_parent));
    return process;
}

Process::Process(NonnullOwnPtr<KString> name, NonnullRefPtr<Credentials> credentials, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, UnveilNode unveil_tree)
    : m_name(move(name))
    , m_space(LockRank::None)
    , m_protected_data_lock(LockRank::None)
    , m_is_kernel_process(is_kernel_process)
    , m_executable(LockRank::None, move(executable))
    , m_current_directory(LockRank::None, move(current_directory))
    , m_tty(tty)
    , m_unveil_data(LockRank::None, move(unveil_tree))
    , m_wait_blocker_set(*this)
{
    // Ensure that we protect the process data when exiting the constructor.
    with_mutable_protected_data([&](auto& protected_data) {
        protected_data.pid = allocate_pid();
        protected_data.ppid = ppid;
        protected_data.credentials = move(credentials);
    });

    dbgln_if(PROCESS_DEBUG, "Created new process {}({})", m_name, this->pid().value());
}

ErrorOr<void> Process::attach_resources(NonnullOwnPtr<Memory::AddressSpace>&& preallocated_space, LockRefPtr<Thread>& first_thread, Process* fork_parent)
{
    m_space.with([&](auto& space) {
        space = move(preallocated_space);
    });

    auto create_first_thread = [&] {
        if (fork_parent) {
            // NOTE: fork() doesn't clone all threads; the thread that called fork() becomes the only thread in the new process.
            return Thread::current()->try_clone(*this);
        }
        // NOTE: This non-forked code path is only taken when the kernel creates a process "manually" (at boot.)
        return Thread::try_create(*this);
    };

    first_thread = TRY(create_first_thread());

    if (!fork_parent) {
        // FIXME: Figure out if this is really necessary.
        first_thread->detach();
    }

    auto weak_ptr = TRY(this->try_make_weak_ptr());
    m_procfs_traits = TRY(ProcessProcFSTraits::try_create({}, move(weak_ptr)));

    // This is not actually explicitly verified by any official documentation,
    // but it's not listed anywhere as being cleared, and rsync expects it to work like this.
    if (fork_parent)
        m_signal_action_data = fork_parent->m_signal_action_data;

    return {};
}

Process::~Process()
{
    unprotect_data();

    VERIFY(thread_count() == 0); // all threads should have been finalized
    VERIFY(!m_alarm_timer);

    PerformanceManager::add_process_exit_event(*this);
}

// Make sure the compiler doesn't "optimize away" this function:
extern void signal_trampoline_dummy() __attribute__((used));
void signal_trampoline_dummy()
{
#if ARCH(I386)
    // The trampoline preserves the current eax, pushes the signal code and
    // then calls the signal handler. We do this because, when interrupting a
    // blocking syscall, that syscall may return some special error code in eax;
    // This error code would likely be overwritten by the signal handler, so it's
    // necessary to preserve it here.
    constexpr static auto offset_to_first_register_slot = sizeof(__ucontext) + sizeof(siginfo) + sizeof(FPUState) + 4 * sizeof(FlatPtr);
    asm(
        ".intel_syntax noprefix\n"
        ".globl asm_signal_trampoline\n"
        "asm_signal_trampoline:\n"
        // stack state: 0, ucontext, signal_info, (alignment = 16), fpu_state (alignment = 16), 0, ucontext*, siginfo*, signal, (alignment = 16), handler

        // Pop the handler into ecx
        "pop ecx\n" // save handler
        // we have to save eax 'cause it might be the return value from a syscall
        "mov [esp+%P1], eax\n"
        // Note that the stack is currently aligned to 16 bytes as we popped the extra entries above.
        // and it's already setup to call the handler with the expected values on the stack.
        // call the signal handler
        "call ecx\n"
        // drop the 4 arguments
        "add esp, 16\n"
        // Current stack state is just saved_eax, ucontext, signal_info, fpu_state?.
        // syscall SC_sigreturn
        "mov eax, %P0\n"
        "int 0x82\n"
        ".globl asm_signal_trampoline_end\n"
        "asm_signal_trampoline_end:\n"
        ".att_syntax"
        :
        : "i"(Syscall::SC_sigreturn),
        "i"(offset_to_first_register_slot));
#elif ARCH(X86_64)
    // The trampoline preserves the current rax, pushes the signal code and
    // then calls the signal handler. We do this because, when interrupting a
    // blocking syscall, that syscall may return some special error code in eax;
    // This error code would likely be overwritten by the signal handler, so it's
    // necessary to preserve it here.
    constexpr static auto offset_to_first_register_slot = sizeof(__ucontext) + sizeof(siginfo) + sizeof(FPUState) + 3 * sizeof(FlatPtr);
    asm(
        ".intel_syntax noprefix\n"
        ".globl asm_signal_trampoline\n"
        "asm_signal_trampoline:\n"
        // stack state: 0, ucontext, signal_info (alignment = 16), fpu_state (alignment = 16), ucontext*, siginfo*, signal, handler

        // Pop the handler into rcx
        "pop rcx\n" // save handler
        // we have to save rax 'cause it might be the return value from a syscall
        "mov [rsp+%P1], rax\n"
        // pop signal number into rdi (first param)
        "pop rdi\n"
        // pop siginfo* into rsi (second param)
        "pop rsi\n"
        // pop ucontext* into rdx (third param)
        "pop rdx\n"
        // Note that the stack is currently aligned to 16 bytes as we popped the extra entries above.
        // call the signal handler
        "call rcx\n"
        // Current stack state is just saved_rax, ucontext, signal_info, fpu_state.
        // syscall SC_sigreturn
        "mov rax, %P0\n"
        "int 0x82\n"
        ".globl asm_signal_trampoline_end\n"
        "asm_signal_trampoline_end:\n"
        ".att_syntax"
        :
        : "i"(Syscall::SC_sigreturn),
        "i"(offset_to_first_register_slot));
#endif
}

extern "C" char const asm_signal_trampoline[];
extern "C" char const asm_signal_trampoline_end[];

void create_signal_trampoline()
{
    // NOTE: We leak this region.
    g_signal_trampoline_region = MM.allocate_kernel_region(PAGE_SIZE, "Signal trampolines"sv, Memory::Region::Access::ReadWrite).release_value().leak_ptr();
    g_signal_trampoline_region->set_syscall_region(true);

    size_t trampoline_size = asm_signal_trampoline_end - asm_signal_trampoline;

    u8* code_ptr = (u8*)g_signal_trampoline_region->vaddr().as_ptr();
    memcpy(code_ptr, asm_signal_trampoline, trampoline_size);

    g_signal_trampoline_region->set_writable(false);
    g_signal_trampoline_region->remap();
}

void Process::crash(int signal, FlatPtr ip, bool out_of_memory)
{
    VERIFY(!is_dead());
    VERIFY(&Process::current() == this);

    if (out_of_memory) {
        dbgln("\033[31;1mOut of memory\033[m, killing: {}", *this);
    } else {
        if (ip >= kernel_load_base && g_kernel_symbols_available) {
            auto const* symbol = symbolicate_kernel_address(ip);
            dbgln("\033[31;1m{:p}  {} +{}\033[0m\n", ip, (symbol ? symbol->name : "(k?)"), (symbol ? ip - symbol->address : 0));
        } else {
            dbgln("\033[31;1m{:p}  (?)\033[0m\n", ip);
        }
        dump_backtrace();
    }
    with_mutable_protected_data([&](auto& protected_data) {
        protected_data.termination_signal = signal;
    });
    set_should_generate_coredump(!out_of_memory);
    address_space().with([](auto& space) { space->dump_regions(); });
    VERIFY(is_user_process());
    die();
    // We can not return from here, as there is nowhere
    // to unwind to, so die right away.
    Thread::current()->die_if_needed();
    VERIFY_NOT_REACHED();
}

LockRefPtr<Process> Process::from_pid(ProcessID pid)
{
    return all_instances().with([&](auto const& list) -> LockRefPtr<Process> {
        for (auto const& process : list) {
            if (process.pid() == pid)
                return &process;
        }
        return {};
    });
}

Process::OpenFileDescriptionAndFlags const* Process::OpenFileDescriptions::get_if_valid(size_t i) const
{
    if (m_fds_metadatas.size() <= i)
        return nullptr;

    if (auto const& metadata = m_fds_metadatas[i]; metadata.is_valid())
        return &metadata;

    return nullptr;
}
Process::OpenFileDescriptionAndFlags* Process::OpenFileDescriptions::get_if_valid(size_t i)
{
    if (m_fds_metadatas.size() <= i)
        return nullptr;

    if (auto& metadata = m_fds_metadatas[i]; metadata.is_valid())
        return &metadata;

    return nullptr;
}

Process::OpenFileDescriptionAndFlags const& Process::OpenFileDescriptions::at(size_t i) const
{
    VERIFY(m_fds_metadatas[i].is_allocated());
    return m_fds_metadatas[i];
}

Process::OpenFileDescriptionAndFlags& Process::OpenFileDescriptions::at(size_t i)
{
    VERIFY(m_fds_metadatas[i].is_allocated());
    return m_fds_metadatas[i];
}

ErrorOr<NonnullLockRefPtr<OpenFileDescription>> Process::OpenFileDescriptions::open_file_description(int fd) const
{
    if (fd < 0)
        return EBADF;
    if (static_cast<size_t>(fd) >= m_fds_metadatas.size())
        return EBADF;
    LockRefPtr description = m_fds_metadatas[fd].description();
    if (!description)
        return EBADF;
    return description.release_nonnull();
}

void Process::OpenFileDescriptions::enumerate(Function<void(OpenFileDescriptionAndFlags const&)> callback) const
{
    for (auto const& file_description_metadata : m_fds_metadatas) {
        callback(file_description_metadata);
    }
}

ErrorOr<void> Process::OpenFileDescriptions::try_enumerate(Function<ErrorOr<void>(OpenFileDescriptionAndFlags const&)> callback) const
{
    for (auto const& file_description_metadata : m_fds_metadatas) {
        TRY(callback(file_description_metadata));
    }
    return {};
}

void Process::OpenFileDescriptions::change_each(Function<void(OpenFileDescriptionAndFlags&)> callback)
{
    for (auto& file_description_metadata : m_fds_metadatas) {
        callback(file_description_metadata);
    }
}

size_t Process::OpenFileDescriptions::open_count() const
{
    size_t count = 0;
    enumerate([&](auto& file_description_metadata) {
        if (file_description_metadata.is_valid())
            ++count;
    });
    return count;
}

ErrorOr<Process::ScopedDescriptionAllocation> Process::OpenFileDescriptions::allocate(int first_candidate_fd)
{
    for (size_t i = first_candidate_fd; i < max_open(); ++i) {
        if (!m_fds_metadatas[i].is_allocated()) {
            m_fds_metadatas[i].allocate();
            return Process::ScopedDescriptionAllocation { static_cast<int>(i), &m_fds_metadatas[i] };
        }
    }
    return EMFILE;
}

Time kgettimeofday()
{
    return TimeManagement::now();
}

siginfo_t Process::wait_info() const
{
    auto credentials = this->credentials();
    siginfo_t siginfo {};
    siginfo.si_signo = SIGCHLD;
    siginfo.si_pid = pid().value();
    siginfo.si_uid = credentials->uid().value();

    with_protected_data([&](auto& protected_data) {
        if (protected_data.termination_signal != 0) {
            siginfo.si_status = protected_data.termination_signal;
            siginfo.si_code = CLD_KILLED;
        } else {
            siginfo.si_status = protected_data.termination_status;
            siginfo.si_code = CLD_EXITED;
        }
    });
    return siginfo;
}

NonnullRefPtr<Custody> Process::current_directory()
{
    return m_current_directory.with([&](auto& current_directory) -> NonnullRefPtr<Custody> {
        if (!current_directory)
            current_directory = VirtualFileSystem::the().root_custody();
        return *current_directory;
    });
}

ErrorOr<NonnullOwnPtr<KString>> Process::get_syscall_path_argument(Userspace<char const*> user_path, size_t path_length)
{
    if (path_length == 0)
        return EINVAL;
    if (path_length > PATH_MAX)
        return ENAMETOOLONG;
    return try_copy_kstring_from_user(user_path, path_length);
}

ErrorOr<NonnullOwnPtr<KString>> Process::get_syscall_path_argument(Syscall::StringArgument const& path)
{
    Userspace<char const*> path_characters((FlatPtr)path.characters);
    return get_syscall_path_argument(path_characters, path.length);
}

ErrorOr<void> Process::dump_core()
{
    VERIFY(is_dumpable());
    VERIFY(should_generate_coredump());
    dbgln("Generating coredump for pid: {}", pid().value());
    auto coredump_path = TRY(KString::formatted("/tmp/coredump/{}_{}_{}", name(), pid().value(), kgettimeofday().to_truncated_seconds()));
    auto coredump = TRY(Coredump::try_create(*this, coredump_path->view()));
    return coredump->write();
}

ErrorOr<void> Process::dump_perfcore()
{
    VERIFY(is_dumpable());
    VERIFY(m_perf_event_buffer);
    dbgln("Generating perfcore for pid: {}", pid().value());

    // Try to generate a filename which isn't already used.
    auto base_filename = TRY(KString::formatted("{}_{}", name(), pid().value()));
    auto perfcore_filename = TRY(KString::formatted("{}.profile", base_filename));
    LockRefPtr<OpenFileDescription> description;
    auto credentials = this->credentials();
    for (size_t attempt = 1; attempt <= 10; ++attempt) {
        auto description_or_error = VirtualFileSystem::the().open(credentials, perfcore_filename->view(), O_CREAT | O_EXCL, 0400, current_directory(), UidAndGid { 0, 0 });
        if (!description_or_error.is_error()) {
            description = description_or_error.release_value();
            break;
        }
        perfcore_filename = TRY(KString::formatted("{}.{}.profile", base_filename, attempt));
    }
    if (!description) {
        dbgln("Failed to generate perfcore for pid {}: Could not generate filename for the perfcore file.", pid().value());
        return EEXIST;
    }

    auto builder = TRY(KBufferBuilder::try_create());
    TRY(m_perf_event_buffer->to_json(builder));

    auto json = builder.build();
    if (!json) {
        dbgln("Failed to generate perfcore for pid {}: Could not allocate buffer.", pid().value());
        return ENOMEM;
    }
    auto json_buffer = UserOrKernelBuffer::for_kernel_buffer(json->data());
    TRY(description->write(json_buffer, json->size()));

    dbgln("Wrote perfcore for pid {} to {}", pid().value(), perfcore_filename);
    return {};
}

void Process::finalize()
{
    VERIFY(Thread::current() == g_finalizer);

    dbgln_if(PROCESS_DEBUG, "Finalizing process {}", *this);

    if (veil_state() == VeilState::Dropped)
        dbgln("\x1b[01;31mProcess '{}' exited with the veil left open\x1b[0m", name());

    if (g_init_pid != 0 && pid() == g_init_pid)
        PANIC("Init process quit unexpectedly. Exit code: {}", termination_status());

    if (is_dumpable()) {
        if (m_should_generate_coredump) {
            auto result = dump_core();
            if (result.is_error()) {
                dmesgln("Failed to write coredump for pid {}: {}", pid(), result.error());
            }
        }
        if (m_perf_event_buffer) {
            auto result = dump_perfcore();
            if (result.is_error())
                dmesgln("Failed to write perfcore for pid {}: {}", pid(), result.error());
            TimeManagement::the().disable_profile_timer();
        }
    }

    m_threads_for_coredump.clear();

    if (m_alarm_timer)
        TimerQueue::the().cancel_timer(m_alarm_timer.release_nonnull());
    m_fds.with_exclusive([](auto& fds) { fds.clear(); });
    m_tty = nullptr;
    m_executable.with([](auto& executable) { executable = nullptr; });
    m_arguments.clear();
    m_environment.clear();

    m_state.store(State::Dead, AK::MemoryOrder::memory_order_release);

    {
        if (auto parent_process = Process::from_pid(ppid())) {
            if (parent_process->is_user_process() && (parent_process->m_signal_action_data[SIGCHLD].flags & SA_NOCLDWAIT) != SA_NOCLDWAIT)
                (void)parent_process->send_signal(SIGCHLD, this);
        }
    }

    if (!!ppid()) {
        if (auto parent = Process::from_pid(ppid())) {
            parent->m_ticks_in_user_for_dead_children += m_ticks_in_user + m_ticks_in_user_for_dead_children;
            parent->m_ticks_in_kernel_for_dead_children += m_ticks_in_kernel + m_ticks_in_kernel_for_dead_children;
        }
    }

    unblock_waiters(Thread::WaitBlocker::UnblockFlags::Terminated);

    m_space.with([](auto& space) { space->remove_all_regions({}); });

    VERIFY(ref_count() > 0);
    // WaitBlockerSet::finalize will be in charge of dropping the last
    // reference if there are still waiters around, or whenever the last
    // waitable states are consumed. Unless there is no parent around
    // anymore, in which case we'll just drop it right away.
    m_wait_blocker_set.finalize();
}

void Process::disowned_by_waiter(Process& process)
{
    m_wait_blocker_set.disowned_by_waiter(process);
}

void Process::unblock_waiters(Thread::WaitBlocker::UnblockFlags flags, u8 signal)
{
    LockRefPtr<Process> waiter_process;
    if (auto* my_tracer = tracer())
        waiter_process = Process::from_pid(my_tracer->tracer_pid());
    else
        waiter_process = Process::from_pid(ppid());

    if (waiter_process)
        waiter_process->m_wait_blocker_set.unblock(*this, flags, signal);
}

void Process::die()
{
    auto expected = State::Running;
    if (!m_state.compare_exchange_strong(expected, State::Dying, AK::memory_order_acquire)) {
        // It's possible that another thread calls this at almost the same time
        // as we can't always instantly kill other threads (they may be blocked)
        // So if we already were called then other threads should stop running
        // momentarily and we only really need to service the first thread
        return;
    }

    // Let go of the TTY, otherwise a slave PTY may keep the master PTY from
    // getting an EOF when the last process using the slave PTY dies.
    // If the master PTY owner relies on an EOF to know when to wait() on a
    // slave owner, we have to allow the PTY pair to be torn down.
    m_tty = nullptr;

    VERIFY(m_threads_for_coredump.is_empty());
    for_each_thread([&](auto& thread) {
        auto result = m_threads_for_coredump.try_append(thread);
        if (result.is_error())
            dbgln("Failed to add thread {} to coredump due to OOM", thread.tid());
    });

    all_instances().with([&](auto const& list) {
        for (auto it = list.begin(); it != list.end();) {
            auto& process = *it;
            ++it;
            if (process.has_tracee_thread(pid())) {
                dbgln_if(PROCESS_DEBUG, "Process {} ({}) is attached by {} ({}) which will exit", process.name(), process.pid(), name(), pid());
                process.stop_tracing();
                auto err = process.send_signal(SIGSTOP, this);
                if (err.is_error())
                    dbgln("Failed to send the SIGSTOP signal to {} ({})", process.name(), process.pid());
            }
        }
    });

    kill_all_threads();
#ifdef ENABLE_KERNEL_COVERAGE_COLLECTION
    KCOVDevice::free_process();
#endif
}

void Process::terminate_due_to_signal(u8 signal)
{
    VERIFY_INTERRUPTS_DISABLED();
    VERIFY(signal < NSIG);
    VERIFY(&Process::current() == this);
    dbgln("Terminating {} due to signal {}", *this, signal);
    with_mutable_protected_data([&](auto& protected_data) {
        protected_data.termination_status = 0;
        protected_data.termination_signal = signal;
    });
    die();
}

ErrorOr<void> Process::send_signal(u8 signal, Process* sender)
{
    VERIFY(is_user_process());
    // Try to send it to the "obvious" main thread:
    auto receiver_thread = Thread::from_tid(pid().value());
    // If the main thread has died, there may still be other threads:
    if (!receiver_thread) {
        // The first one should be good enough.
        // Neither kill(2) nor kill(3) specify any selection procedure.
        for_each_thread([&receiver_thread](Thread& thread) -> IterationDecision {
            receiver_thread = &thread;
            return IterationDecision::Break;
        });
    }
    if (receiver_thread) {
        receiver_thread->send_signal(signal, sender);
        return {};
    }
    return ESRCH;
}

LockRefPtr<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));

    // FIXME: Do something with guard pages?

    auto thread_or_error = Thread::try_create(*this);
    if (thread_or_error.is_error())
        return {};

    auto thread = thread_or_error.release_value();
    thread->set_name(move(name));
    thread->set_affinity(affinity);
    thread->set_priority(priority);
    if (!joinable)
        thread->detach();

    auto& regs = thread->regs();
    regs.set_ip((FlatPtr)entry);
    regs.set_sp((FlatPtr)entry_data); // entry function argument is expected to be in the SP register

    SpinlockLocker lock(g_scheduler_lock);
    thread->set_state(Thread::State::Runnable);
    return thread;
}

void Process::OpenFileDescriptionAndFlags::clear()
{
    // FIXME: Verify Process::m_fds_lock is locked!
    m_description = nullptr;
    m_flags = 0;
}

void Process::OpenFileDescriptionAndFlags::set(NonnullLockRefPtr<OpenFileDescription>&& description, u32 flags)
{
    // FIXME: Verify Process::m_fds_lock is locked!
    m_description = move(description);
    m_flags = flags;
}

void Process::set_tty(TTY* tty)
{
    m_tty = tty;
}

ErrorOr<void> Process::start_tracing_from(ProcessID tracer)
{
    m_tracer = TRY(ThreadTracer::try_create(tracer));
    return {};
}

void Process::stop_tracing()
{
    m_tracer = nullptr;
}

void Process::tracer_trap(Thread& thread, RegisterState const& regs)
{
    VERIFY(m_tracer.ptr());
    m_tracer->set_regs(regs);
    thread.send_urgent_signal_to_self(SIGTRAP);
}

bool Process::create_perf_events_buffer_if_needed()
{
    if (m_perf_event_buffer)
        return true;
    m_perf_event_buffer = PerformanceEventBuffer::try_create_with_size(4 * MiB);
    if (!m_perf_event_buffer)
        return false;
    return !m_perf_event_buffer->add_process(*this, ProcessEventType::Create).is_error();
}

void Process::delete_perf_events_buffer()
{
    if (m_perf_event_buffer)
        m_perf_event_buffer = nullptr;
}

bool Process::remove_thread(Thread& thread)
{
    u32 thread_count_before = 0;
    thread_list().with([&](auto& thread_list) {
        thread_list.remove(thread);
        with_mutable_protected_data([&](auto& protected_data) {
            thread_count_before = protected_data.thread_count.fetch_sub(1, AK::MemoryOrder::memory_order_acq_rel);
            VERIFY(thread_count_before != 0);
        });
    });
    return thread_count_before == 1;
}

bool Process::add_thread(Thread& thread)
{
    bool is_first = false;
    thread_list().with([&](auto& thread_list) {
        thread_list.append(thread);
        with_mutable_protected_data([&](auto& protected_data) {
            is_first = protected_data.thread_count.fetch_add(1, AK::MemoryOrder::memory_order_relaxed) == 0;
        });
    });
    return is_first;
}

void Process::set_dumpable(bool dumpable)
{
    with_mutable_protected_data([&](auto& protected_data) {
        protected_data.dumpable = dumpable;
    });
}

ErrorOr<void> Process::set_coredump_property(NonnullOwnPtr<KString> key, NonnullOwnPtr<KString> value)
{
    return m_coredump_properties.with([&](auto& coredump_properties) -> ErrorOr<void> {
        // Write it into the first available property slot.
        for (auto& slot : coredump_properties) {
            if (slot.key)
                continue;
            slot.key = move(key);
            slot.value = move(value);
            return {};
        }

        return ENOBUFS;
    });
}

ErrorOr<void> Process::try_set_coredump_property(StringView key, StringView value)
{
    auto key_kstring = TRY(KString::try_create(key));
    auto value_kstring = TRY(KString::try_create(value));
    return set_coredump_property(move(key_kstring), move(value_kstring));
};

static constexpr StringView to_string(Pledge promise)
{
#define __ENUMERATE_PLEDGE_PROMISE(x) \
    case Pledge::x:                   \
        return #x##sv;
    switch (promise) {
        ENUMERATE_PLEDGE_PROMISES
    }
#undef __ENUMERATE_PLEDGE_PROMISE
    VERIFY_NOT_REACHED();
}

ErrorOr<void> Process::require_no_promises() const
{
    if (!has_promises())
        return {};
    dbgln("Has made a promise");
    Thread::current()->set_promise_violation_pending(true);
    return EPROMISEVIOLATION;
}

ErrorOr<void> Process::require_promise(Pledge promise)
{
    if (!has_promises())
        return {};

    if (has_promised(promise))
        return {};

    dbgln("Has not pledged {}", to_string(promise));
    Thread::current()->set_promise_violation_pending(true);
    (void)try_set_coredump_property("pledge_violation"sv, to_string(promise));
    return EPROMISEVIOLATION;
}

NonnullRefPtr<Credentials> Process::credentials() const
{
    return with_protected_data([&](auto& protected_data) -> NonnullRefPtr<Credentials> {
        return *protected_data.credentials;
    });
}

RefPtr<Custody> Process::executable()
{
    return m_executable.with([](auto& executable) { return executable; });
}

RefPtr<Custody const> Process::executable() const
{
    return m_executable.with([](auto& executable) { return executable; });
}

}