drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / kernel / reboot.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/kernel/reboot.c
 *
 *  Copyright (C) 2013  Linus Torvalds
 */

#define pr_fmt(fmt)     "reboot: " fmt

#include <linux/atomic.h>
#include <linux/ctype.h>
#include <linux/export.h>
#include <linux/kexec.h>
#include <linux/kmod.h>
#include <linux/kmsg_dump.h>
#include <linux/reboot.h>
#include <linux/suspend.h>
#include <linux/syscalls.h>
#include <linux/syscore_ops.h>
#include <linux/uaccess.h>

/*
 * this indicates whether you can reboot with ctrl-alt-del: the default is yes
 */

static int C_A_D = 1;
struct pid *cad_pid;
EXPORT_SYMBOL(cad_pid);

#if defined(CONFIG_ARM)
#define DEFAULT_REBOOT_MODE             = REBOOT_HARD
#else
#define DEFAULT_REBOOT_MODE
#endif
enum reboot_mode reboot_mode DEFAULT_REBOOT_MODE;
EXPORT_SYMBOL_GPL(reboot_mode);
enum reboot_mode panic_reboot_mode = REBOOT_UNDEFINED;

/*
 * This variable is used privately to keep track of whether or not
 * reboot_type is still set to its default value (i.e., reboot= hasn't
 * been set on the command line).  This is needed so that we can
 * suppress DMI scanning for reboot quirks.  Without it, it's
 * impossible to override a faulty reboot quirk without recompiling.
 */
int reboot_default = 1;
int reboot_cpu;
enum reboot_type reboot_type = BOOT_ACPI;
int reboot_force;

struct sys_off_handler {
        struct notifier_block nb;
        int (*sys_off_cb)(struct sys_off_data *data);
        void *cb_data;
        enum sys_off_mode mode;
        bool blocking;
        void *list;
        struct device *dev;
};

/*
 * This variable is used to indicate if a halt was initiated instead of a
 * reboot when the reboot call was invoked with LINUX_REBOOT_CMD_POWER_OFF, but
 * the system cannot be powered off. This allowes kernel_halt() to notify users
 * of that.
 */
static bool poweroff_fallback_to_halt;

/*
 * Temporary stub that prevents linkage failure while we're in process
 * of removing all uses of legacy pm_power_off() around the kernel.
 */
void __weak (*pm_power_off)(void);

/*
 *      Notifier list for kernel code which wants to be called
 *      at shutdown. This is used to stop any idling DMA operations
 *      and the like.
 */
static BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);

/**
 *      emergency_restart - reboot the system
 *
 *      Without shutting down any hardware or taking any locks
 *      reboot the system.  This is called when we know we are in
 *      trouble so this is our best effort to reboot.  This is
 *      safe to call in interrupt context.
 */
void emergency_restart(void)
{
        kmsg_dump(KMSG_DUMP_EMERG);
        system_state = SYSTEM_RESTART;
        machine_emergency_restart();
}
EXPORT_SYMBOL_GPL(emergency_restart);

void kernel_restart_prepare(char *cmd)
{
        blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);
        system_state = SYSTEM_RESTART;
        usermodehelper_disable();
        device_shutdown();
}

/**
 *      register_reboot_notifier - Register function to be called at reboot time
 *      @nb: Info about notifier function to be called
 *
 *      Registers a function with the list of functions
 *      to be called at reboot time.
 *
 *      Currently always returns zero, as blocking_notifier_chain_register()
 *      always returns zero.
 */
int register_reboot_notifier(struct notifier_block *nb)
{
        return blocking_notifier_chain_register(&reboot_notifier_list, nb);
}
EXPORT_SYMBOL(register_reboot_notifier);

/**
 *      unregister_reboot_notifier - Unregister previously registered reboot notifier
 *      @nb: Hook to be unregistered
 *
 *      Unregisters a previously registered reboot
 *      notifier function.
 *
 *      Returns zero on success, or %-ENOENT on failure.
 */
int unregister_reboot_notifier(struct notifier_block *nb)
{
        return blocking_notifier_chain_unregister(&reboot_notifier_list, nb);
}
EXPORT_SYMBOL(unregister_reboot_notifier);

static void devm_unregister_reboot_notifier(struct device *dev, void *res)
{
        WARN_ON(unregister_reboot_notifier(*(struct notifier_block **)res));
}

int devm_register_reboot_notifier(struct device *dev, struct notifier_block *nb)
{
        struct notifier_block **rcnb;
        int ret;

        rcnb = devres_alloc(devm_unregister_reboot_notifier,
                            sizeof(*rcnb), GFP_KERNEL);
        if (!rcnb)
                return -ENOMEM;

        ret = register_reboot_notifier(nb);
        if (!ret) {
                *rcnb = nb;
                devres_add(dev, rcnb);
        } else {
                devres_free(rcnb);
        }

        return ret;
}
EXPORT_SYMBOL(devm_register_reboot_notifier);

/*
 *      Notifier list for kernel code which wants to be called
 *      to restart the system.
 */
static ATOMIC_NOTIFIER_HEAD(restart_handler_list);

/**
 *      register_restart_handler - Register function to be called to reset
 *                                 the system
 *      @nb: Info about handler function to be called
 *      @nb->priority:  Handler priority. Handlers should follow the
 *                      following guidelines for setting priorities.
 *                      0:      Restart handler of last resort,
 *                              with limited restart capabilities
 *                      128:    Default restart handler; use if no other
 *                              restart handler is expected to be available,
 *                              and/or if restart functionality is
 *                              sufficient to restart the entire system
 *                      255:    Highest priority restart handler, will
 *                              preempt all other restart handlers
 *
 *      Registers a function with code to be called to restart the
 *      system.
 *
 *      Registered functions will be called from machine_restart as last
 *      step of the restart sequence (if the architecture specific
 *      machine_restart function calls do_kernel_restart - see below
 *      for details).
 *      Registered functions are expected to restart the system immediately.
 *      If more than one function is registered, the restart handler priority
 *      selects which function will be called first.
 *
 *      Restart handlers are expected to be registered from non-architecture
 *      code, typically from drivers. A typical use case would be a system
 *      where restart functionality is provided through a watchdog. Multiple
 *      restart handlers may exist; for example, one restart handler might
 *      restart the entire system, while another only restarts the CPU.
 *      In such cases, the restart handler which only restarts part of the
 *      hardware is expected to register with low priority to ensure that
 *      it only runs if no other means to restart the system is available.
 *
 *      Currently always returns zero, as atomic_notifier_chain_register()
 *      always returns zero.
 */
int register_restart_handler(struct notifier_block *nb)
{
        return atomic_notifier_chain_register(&restart_handler_list, nb);
}
EXPORT_SYMBOL(register_restart_handler);

/**
 *      unregister_restart_handler - Unregister previously registered
 *                                   restart handler
 *      @nb: Hook to be unregistered
 *
 *      Unregisters a previously registered restart handler function.
 *
 *      Returns zero on success, or %-ENOENT on failure.
 */
int unregister_restart_handler(struct notifier_block *nb)
{
        return atomic_notifier_chain_unregister(&restart_handler_list, nb);
}
EXPORT_SYMBOL(unregister_restart_handler);

/**
 *      do_kernel_restart - Execute kernel restart handler call chain
 *
 *      Calls functions registered with register_restart_handler.
 *
 *      Expected to be called from machine_restart as last step of the restart
 *      sequence.
 *
 *      Restarts the system immediately if a restart handler function has been
 *      registered. Otherwise does nothing.
 */
void do_kernel_restart(char *cmd)
{
        atomic_notifier_call_chain(&restart_handler_list, reboot_mode, cmd);
}

void migrate_to_reboot_cpu(void)
{
        /* The boot cpu is always logical cpu 0 */
        int cpu = reboot_cpu;

        cpu_hotplug_disable();

        /* Make certain the cpu I'm about to reboot on is online */
        if (!cpu_online(cpu))
                cpu = cpumask_first(cpu_online_mask);

        /* Prevent races with other tasks migrating this task */
        current->flags |= PF_NO_SETAFFINITY;

        /* Make certain I only run on the appropriate processor */
        set_cpus_allowed_ptr(current, cpumask_of(cpu));
}

/*
 *      Notifier list for kernel code which wants to be called
 *      to prepare system for restart.
 */
static BLOCKING_NOTIFIER_HEAD(restart_prep_handler_list);

static void do_kernel_restart_prepare(void)
{
        blocking_notifier_call_chain(&restart_prep_handler_list, 0, NULL);
}

/**
 *      kernel_restart - reboot the system
 *      @cmd: pointer to buffer containing command to execute for restart
 *              or %NULL
 *
 *      Shutdown everything and perform a clean reboot.
 *      This is not safe to call in interrupt context.
 */
void kernel_restart(char *cmd)
{
        kernel_restart_prepare(cmd);
        do_kernel_restart_prepare();
        migrate_to_reboot_cpu();
        syscore_shutdown();
        if (!cmd)
                pr_emerg("Restarting system\n");
        else
                pr_emerg("Restarting system with command '%s'\n", cmd);
        kmsg_dump(KMSG_DUMP_SHUTDOWN);
        machine_restart(cmd);
}
EXPORT_SYMBOL_GPL(kernel_restart);

static void kernel_shutdown_prepare(enum system_states state)
{
        blocking_notifier_call_chain(&reboot_notifier_list,
                (state == SYSTEM_HALT) ? SYS_HALT : SYS_POWER_OFF, NULL);
        system_state = state;
        usermodehelper_disable();
        device_shutdown();
}
/**
 *      kernel_halt - halt the system
 *
 *      Shutdown everything and perform a clean system halt.
 */
void kernel_halt(void)
{
        kernel_shutdown_prepare(SYSTEM_HALT);
        migrate_to_reboot_cpu();
        syscore_shutdown();
        if (poweroff_fallback_to_halt)
                pr_emerg("Power off not available: System halted instead\n");
        else
                pr_emerg("System halted\n");
        kmsg_dump(KMSG_DUMP_SHUTDOWN);
        machine_halt();
}
EXPORT_SYMBOL_GPL(kernel_halt);

/*
 *      Notifier list for kernel code which wants to be called
 *      to prepare system for power off.
 */
static BLOCKING_NOTIFIER_HEAD(power_off_prep_handler_list);

/*
 *      Notifier list for kernel code which wants to be called
 *      to power off system.
 */
static ATOMIC_NOTIFIER_HEAD(power_off_handler_list);

static int sys_off_notify(struct notifier_block *nb,
                          unsigned long mode, void *cmd)
{
        struct sys_off_handler *handler;
        struct sys_off_data data = {};

        handler = container_of(nb, struct sys_off_handler, nb);
        data.cb_data = handler->cb_data;
        data.mode = mode;
        data.cmd = cmd;
        data.dev = handler->dev;

        return handler->sys_off_cb(&data);
}

static struct sys_off_handler platform_sys_off_handler;

static struct sys_off_handler *alloc_sys_off_handler(int priority)
{
        struct sys_off_handler *handler;
        gfp_t flags;

        /*
         * Platforms like m68k can't allocate sys_off handler dynamically
         * at the early boot time because memory allocator isn't available yet.
         */
        if (priority == SYS_OFF_PRIO_PLATFORM) {
                handler = &platform_sys_off_handler;
                if (handler->cb_data)
                        return ERR_PTR(-EBUSY);
        } else {
                if (system_state > SYSTEM_RUNNING)
                        flags = GFP_ATOMIC;
                else
                        flags = GFP_KERNEL;

                handler = kzalloc(sizeof(*handler), flags);
                if (!handler)
                        return ERR_PTR(-ENOMEM);
        }

        return handler;
}

static void free_sys_off_handler(struct sys_off_handler *handler)
{
        if (handler == &platform_sys_off_handler)
                memset(handler, 0, sizeof(*handler));
        else
                kfree(handler);
}

/**
 *      register_sys_off_handler - Register sys-off handler
 *      @mode: Sys-off mode
 *      @priority: Handler priority
 *      @callback: Callback function
 *      @cb_data: Callback argument
 *
 *      Registers system power-off or restart handler that will be invoked
 *      at the step corresponding to the given sys-off mode. Handler's callback
 *      should return NOTIFY_DONE to permit execution of the next handler in
 *      the call chain or NOTIFY_STOP to break the chain (in error case for
 *      example).
 *
 *      Multiple handlers can be registered at the default priority level.
 *
 *      Only one handler can be registered at the non-default priority level,
 *      otherwise ERR_PTR(-EBUSY) is returned.
 *
 *      Returns a new instance of struct sys_off_handler on success, or
 *      an ERR_PTR()-encoded error code otherwise.
 */
struct sys_off_handler *
register_sys_off_handler(enum sys_off_mode mode,
                         int priority,
                         int (*callback)(struct sys_off_data *data),
                         void *cb_data)
{
        struct sys_off_handler *handler;
        int err;

        handler = alloc_sys_off_handler(priority);
        if (IS_ERR(handler))
                return handler;

        switch (mode) {
        case SYS_OFF_MODE_POWER_OFF_PREPARE:
                handler->list = &power_off_prep_handler_list;
                handler->blocking = true;
                break;

        case SYS_OFF_MODE_POWER_OFF:
                handler->list = &power_off_handler_list;
                break;

        case SYS_OFF_MODE_RESTART_PREPARE:
                handler->list = &restart_prep_handler_list;
                handler->blocking = true;
                break;

        case SYS_OFF_MODE_RESTART:
                handler->list = &restart_handler_list;
                break;

        default:
                free_sys_off_handler(handler);
                return ERR_PTR(-EINVAL);
        }

        handler->nb.notifier_call = sys_off_notify;
        handler->nb.priority = priority;
        handler->sys_off_cb = callback;
        handler->cb_data = cb_data;
        handler->mode = mode;

        if (handler->blocking) {
                if (priority == SYS_OFF_PRIO_DEFAULT)
                        err = blocking_notifier_chain_register(handler->list,
                                                               &handler->nb);
                else
                        err = blocking_notifier_chain_register_unique_prio(handler->list,
                                                                           &handler->nb);
        } else {
                if (priority == SYS_OFF_PRIO_DEFAULT)
                        err = atomic_notifier_chain_register(handler->list,
                                                             &handler->nb);
                else
                        err = atomic_notifier_chain_register_unique_prio(handler->list,
                                                                         &handler->nb);
        }

        if (err) {
                free_sys_off_handler(handler);
                return ERR_PTR(err);
        }

        return handler;
}
EXPORT_SYMBOL_GPL(register_sys_off_handler);

/**
 *      unregister_sys_off_handler - Unregister sys-off handler
 *      @handler: Sys-off handler
 *
 *      Unregisters given sys-off handler.
 */
void unregister_sys_off_handler(struct sys_off_handler *handler)
{
        int err;

        if (IS_ERR_OR_NULL(handler))
                return;

        if (handler->blocking)
                err = blocking_notifier_chain_unregister(handler->list,
                                                         &handler->nb);
        else
                err = atomic_notifier_chain_unregister(handler->list,
                                                       &handler->nb);

        /* sanity check, shall never happen */
        WARN_ON(err);

        free_sys_off_handler(handler);
}
EXPORT_SYMBOL_GPL(unregister_sys_off_handler);

static void devm_unregister_sys_off_handler(void *data)
{
        struct sys_off_handler *handler = data;

        unregister_sys_off_handler(handler);
}

/**
 *      devm_register_sys_off_handler - Register sys-off handler
 *      @dev: Device that registers handler
 *      @mode: Sys-off mode
 *      @priority: Handler priority
 *      @callback: Callback function
 *      @cb_data: Callback argument
 *
 *      Registers resource-managed sys-off handler.
 *
 *      Returns zero on success, or error code on failure.
 */
int devm_register_sys_off_handler(struct device *dev,
                                  enum sys_off_mode mode,
                                  int priority,
                                  int (*callback)(struct sys_off_data *data),
                                  void *cb_data)
{
        struct sys_off_handler *handler;

        handler = register_sys_off_handler(mode, priority, callback, cb_data);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        handler->dev = dev;

        return devm_add_action_or_reset(dev, devm_unregister_sys_off_handler,
                                        handler);
}
EXPORT_SYMBOL_GPL(devm_register_sys_off_handler);

/**
 *      devm_register_power_off_handler - Register power-off handler
 *      @dev: Device that registers callback
 *      @callback: Callback function
 *      @cb_data: Callback's argument
 *
 *      Registers resource-managed sys-off handler with a default priority
 *      and using power-off mode.
 *
 *      Returns zero on success, or error code on failure.
 */
int devm_register_power_off_handler(struct device *dev,
                                    int (*callback)(struct sys_off_data *data),
                                    void *cb_data)
{
        return devm_register_sys_off_handler(dev,
                                             SYS_OFF_MODE_POWER_OFF,
                                             SYS_OFF_PRIO_DEFAULT,
                                             callback, cb_data);
}
EXPORT_SYMBOL_GPL(devm_register_power_off_handler);

/**
 *      devm_register_restart_handler - Register restart handler
 *      @dev: Device that registers callback
 *      @callback: Callback function
 *      @cb_data: Callback's argument
 *
 *      Registers resource-managed sys-off handler with a default priority
 *      and using restart mode.
 *
 *      Returns zero on success, or error code on failure.
 */
int devm_register_restart_handler(struct device *dev,
                                  int (*callback)(struct sys_off_data *data),
                                  void *cb_data)
{
        return devm_register_sys_off_handler(dev,
                                             SYS_OFF_MODE_RESTART,
                                             SYS_OFF_PRIO_DEFAULT,
                                             callback, cb_data);
}
EXPORT_SYMBOL_GPL(devm_register_restart_handler);

static struct sys_off_handler *platform_power_off_handler;

static int platform_power_off_notify(struct sys_off_data *data)
{
        void (*platform_power_power_off_cb)(void) = data->cb_data;

        platform_power_power_off_cb();

        return NOTIFY_DONE;
}

/**
 *      register_platform_power_off - Register platform-level power-off callback
 *      @power_off: Power-off callback
 *
 *      Registers power-off callback that will be called as last step
 *      of the power-off sequence. This callback is expected to be invoked
 *      for the last resort. Only one platform power-off callback is allowed
 *      to be registered at a time.
 *
 *      Returns zero on success, or error code on failure.
 */
int register_platform_power_off(void (*power_off)(void))
{
        struct sys_off_handler *handler;

        handler = register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
                                           SYS_OFF_PRIO_PLATFORM,
                                           platform_power_off_notify,
                                           power_off);
        if (IS_ERR(handler))
                return PTR_ERR(handler);

        platform_power_off_handler = handler;

        return 0;
}
EXPORT_SYMBOL_GPL(register_platform_power_off);

/**
 *      unregister_platform_power_off - Unregister platform-level power-off callback
 *      @power_off: Power-off callback
 *
 *      Unregisters previously registered platform power-off callback.
 */
void unregister_platform_power_off(void (*power_off)(void))
{
        if (platform_power_off_handler &&
            platform_power_off_handler->cb_data == power_off) {
                unregister_sys_off_handler(platform_power_off_handler);
                platform_power_off_handler = NULL;
        }
}
EXPORT_SYMBOL_GPL(unregister_platform_power_off);

static int legacy_pm_power_off(struct sys_off_data *data)
{
        if (pm_power_off)
                pm_power_off();

        return NOTIFY_DONE;
}

static void do_kernel_power_off_prepare(void)
{
        blocking_notifier_call_chain(&power_off_prep_handler_list, 0, NULL);
}

/**
 *      do_kernel_power_off - Execute kernel power-off handler call chain
 *
 *      Expected to be called as last step of the power-off sequence.
 *
 *      Powers off the system immediately if a power-off handler function has
 *      been registered. Otherwise does nothing.
 */
void do_kernel_power_off(void)
{
        struct sys_off_handler *sys_off = NULL;

        /*
         * Register sys-off handlers for legacy PM callback. This allows
         * legacy PM callbacks temporary co-exist with the new sys-off API.
         *
         * TODO: Remove legacy handlers once all legacy PM users will be
         *       switched to the sys-off based APIs.
         */
        if (pm_power_off)
                sys_off = register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
                                                   SYS_OFF_PRIO_DEFAULT,
                                                   legacy_pm_power_off, NULL);

        atomic_notifier_call_chain(&power_off_handler_list, 0, NULL);

        unregister_sys_off_handler(sys_off);
}

/**
 *      kernel_can_power_off - check whether system can be powered off
 *
 *      Returns true if power-off handler is registered and system can be
 *      powered off, false otherwise.
 */
bool kernel_can_power_off(void)
{
        return !atomic_notifier_call_chain_is_empty(&power_off_handler_list) ||
                pm_power_off;
}
EXPORT_SYMBOL_GPL(kernel_can_power_off);

/**
 *      kernel_power_off - power_off the system
 *
 *      Shutdown everything and perform a clean system power_off.
 */
void kernel_power_off(void)
{
        kernel_shutdown_prepare(SYSTEM_POWER_OFF);
        do_kernel_power_off_prepare();
        migrate_to_reboot_cpu();
        syscore_shutdown();
        pr_emerg("Power down\n");
        kmsg_dump(KMSG_DUMP_SHUTDOWN);
        machine_power_off();
}
EXPORT_SYMBOL_GPL(kernel_power_off);

DEFINE_MUTEX(system_transition_mutex);

/*
 * Reboot system call: for obvious reasons only root may call it,
 * and even root needs to set up some magic numbers in the registers
 * so that some mistake won't make this reboot the whole machine.
 * You can also set the meaning of the ctrl-alt-del-key here.
 *
 * reboot doesn't sync: do that yourself before calling this.
 */
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
                void __user *, arg)
{
        struct pid_namespace *pid_ns = task_active_pid_ns(current);
        char buffer[256];
        int ret = 0;

        /* We only trust the superuser with rebooting the system. */
        if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))
                return -EPERM;

        /* For safety, we require "magic" arguments. */
        if (magic1 != LINUX_REBOOT_MAGIC1 ||
                        (magic2 != LINUX_REBOOT_MAGIC2 &&
                        magic2 != LINUX_REBOOT_MAGIC2A &&
                        magic2 != LINUX_REBOOT_MAGIC2B &&
                        magic2 != LINUX_REBOOT_MAGIC2C))
                return -EINVAL;

        /*
         * If pid namespaces are enabled and the current task is in a child
         * pid_namespace, the command is handled by reboot_pid_ns() which will
         * call do_exit().
         */
        ret = reboot_pid_ns(pid_ns, cmd);
        if (ret)
                return ret;

        /* Instead of trying to make the power_off code look like
         * halt when pm_power_off is not set do it the easy way.
         */
        if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !kernel_can_power_off()) {
                poweroff_fallback_to_halt = true;
                cmd = LINUX_REBOOT_CMD_HALT;
        }

        mutex_lock(&system_transition_mutex);
        switch (cmd) {
        case LINUX_REBOOT_CMD_RESTART:
                kernel_restart(NULL);
                break;

        case LINUX_REBOOT_CMD_CAD_ON:
                C_A_D = 1;
                break;

        case LINUX_REBOOT_CMD_CAD_OFF:
                C_A_D = 0;
                break;

        case LINUX_REBOOT_CMD_HALT:
                kernel_halt();
                do_exit(0);

        case LINUX_REBOOT_CMD_POWER_OFF:
                kernel_power_off();
                do_exit(0);
                break;

        case LINUX_REBOOT_CMD_RESTART2:
                ret = strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1);
                if (ret < 0) {
                        ret = -EFAULT;
                        break;
                }
                buffer[sizeof(buffer) - 1] = '\0';

                kernel_restart(buffer);
                break;

#ifdef CONFIG_KEXEC_CORE
        case LINUX_REBOOT_CMD_KEXEC:
                ret = kernel_kexec();
                break;
#endif

#ifdef CONFIG_HIBERNATION
        case LINUX_REBOOT_CMD_SW_SUSPEND:
                ret = hibernate();
                break;
#endif

        default:
                ret = -EINVAL;
                break;
        }
        mutex_unlock(&system_transition_mutex);
        return ret;
}

static void deferred_cad(struct work_struct *dummy)
{
        kernel_restart(NULL);
}

/*
 * This function gets called by ctrl-alt-del - ie the keyboard interrupt.
 * As it's called within an interrupt, it may NOT sync: the only choice
 * is whether to reboot at once, or just ignore the ctrl-alt-del.
 */
void ctrl_alt_del(void)
{
        static DECLARE_WORK(cad_work, deferred_cad);

        if (C_A_D)
                schedule_work(&cad_work);
        else
                kill_cad_pid(SIGINT, 1);
}

#define POWEROFF_CMD_PATH_LEN  256
static char poweroff_cmd[POWEROFF_CMD_PATH_LEN] = "/sbin/poweroff";
static const char reboot_cmd[] = "/sbin/reboot";

static int run_cmd(const char *cmd)
{
        char **argv;
        static char *envp[] = {
                "HOME=/",
                "PATH=/sbin:/bin:/usr/sbin:/usr/bin",
                NULL
        };
        int ret;
        argv = argv_split(GFP_KERNEL, cmd, NULL);
        if (argv) {
                ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
                argv_free(argv);
        } else {
                ret = -ENOMEM;
        }

        return ret;
}

static int __orderly_reboot(void)
{
        int ret;

        ret = run_cmd(reboot_cmd);

        if (ret) {
                pr_warn("Failed to start orderly reboot: forcing the issue\n");
                emergency_sync();
                kernel_restart(NULL);
        }

        return ret;
}

static int __orderly_poweroff(bool force)
{
        int ret;

        ret = run_cmd(poweroff_cmd);

        if (ret && force) {
                pr_warn("Failed to start orderly shutdown: forcing the issue\n");

                /*
                 * I guess this should try to kick off some daemon to sync and
                 * poweroff asap.  Or not even bother syncing if we're doing an
                 * emergency shutdown?
                 */
                emergency_sync();
                kernel_power_off();
        }

        return ret;
}

static bool poweroff_force;

static void poweroff_work_func(struct work_struct *work)
{
        __orderly_poweroff(poweroff_force);
}

static DECLARE_WORK(poweroff_work, poweroff_work_func);

/**
 * orderly_poweroff - Trigger an orderly system poweroff
 * @force: force poweroff if command execution fails
 *
 * This may be called from any context to trigger a system shutdown.
 * If the orderly shutdown fails, it will force an immediate shutdown.
 */
void orderly_poweroff(bool force)
{
        if (force) /* do not override the pending "true" */
                poweroff_force = true;
        schedule_work(&poweroff_work);
}
EXPORT_SYMBOL_GPL(orderly_poweroff);

static void reboot_work_func(struct work_struct *work)
{
        __orderly_reboot();
}

static DECLARE_WORK(reboot_work, reboot_work_func);

/**
 * orderly_reboot - Trigger an orderly system reboot
 *
 * This may be called from any context to trigger a system reboot.
 * If the orderly reboot fails, it will force an immediate reboot.
 */
void orderly_reboot(void)
{
        schedule_work(&reboot_work);
}
EXPORT_SYMBOL_GPL(orderly_reboot);

/**
 * hw_failure_emergency_poweroff_func - emergency poweroff work after a known delay
 * @work: work_struct associated with the emergency poweroff function
 *
 * This function is called in very critical situations to force
 * a kernel poweroff after a configurable timeout value.
 */
static void hw_failure_emergency_poweroff_func(struct work_struct *work)
{
        /*
         * We have reached here after the emergency shutdown waiting period has
         * expired. This means orderly_poweroff has not been able to shut off
         * the system for some reason.
         *
         * Try to shut down the system immediately using kernel_power_off
         * if populated
         */
        pr_emerg("Hardware protection timed-out. Trying forced poweroff\n");
        kernel_power_off();

        /*
         * Worst of the worst case trigger emergency restart
         */
        pr_emerg("Hardware protection shutdown failed. Trying emergency restart\n");
        emergency_restart();
}

static DECLARE_DELAYED_WORK(hw_failure_emergency_poweroff_work,
                            hw_failure_emergency_poweroff_func);

/**
 * hw_failure_emergency_poweroff - Trigger an emergency system poweroff
 *
 * This may be called from any critical situation to trigger a system shutdown
 * after a given period of time. If time is negative this is not scheduled.
 */
static void hw_failure_emergency_poweroff(int poweroff_delay_ms)
{
        if (poweroff_delay_ms <= 0)
                return;
        schedule_delayed_work(&hw_failure_emergency_poweroff_work,
                              msecs_to_jiffies(poweroff_delay_ms));
}

/**
 * __hw_protection_shutdown - Trigger an emergency system shutdown or reboot
 *
 * @reason:             Reason of emergency shutdown or reboot to be printed.
 * @ms_until_forced:    Time to wait for orderly shutdown or reboot before
 *                      triggering it. Negative value disables the forced
 *                      shutdown or reboot.
 * @shutdown:           If true, indicates that a shutdown will happen
 *                      after the critical tempeature is reached.
 *                      If false, indicates that a reboot will happen
 *                      after the critical tempeature is reached.
 *
 * Initiate an emergency system shutdown or reboot in order to protect
 * hardware from further damage. Usage examples include a thermal protection.
 * NOTE: The request is ignored if protection shutdown or reboot is already
 * pending even if the previous request has given a large timeout for forced
 * shutdown/reboot.
 */
void __hw_protection_shutdown(const char *reason, int ms_until_forced, bool shutdown)
{
        static atomic_t allow_proceed = ATOMIC_INIT(1);

        pr_emerg("HARDWARE PROTECTION shutdown (%s)\n", reason);

        /* Shutdown should be initiated only once. */
        if (!atomic_dec_and_test(&allow_proceed))
                return;

        /*
         * Queue a backup emergency shutdown in the event of
         * orderly_poweroff failure
         */
        hw_failure_emergency_poweroff(ms_until_forced);
        if (shutdown)
                orderly_poweroff(true);
        else
                orderly_reboot();
}
EXPORT_SYMBOL_GPL(__hw_protection_shutdown);

static int __init reboot_setup(char *str)
{
        for (;;) {
                enum reboot_mode *mode;

                /*
                 * Having anything passed on the command line via
                 * reboot= will cause us to disable DMI checking
                 * below.
                 */
                reboot_default = 0;

                if (!strncmp(str, "panic_", 6)) {
                        mode = &panic_reboot_mode;
                        str += 6;
                } else {
                        mode = &reboot_mode;
                }

                switch (*str) {
                case 'w':
                        *mode = REBOOT_WARM;
                        break;

                case 'c':
                        *mode = REBOOT_COLD;
                        break;

                case 'h':
                        *mode = REBOOT_HARD;
                        break;

                case 's':
                        /*
                         * reboot_cpu is s[mp]#### with #### being the processor
                         * to be used for rebooting. Skip 's' or 'smp' prefix.
                         */
                        str += str[1] == 'm' && str[2] == 'p' ? 3 : 1;

                        if (isdigit(str[0])) {
                                int cpu = simple_strtoul(str, NULL, 0);

                                if (cpu >= num_possible_cpus()) {
                                        pr_err("Ignoring the CPU number in reboot= option. "
                                        "CPU %d exceeds possible cpu number %d\n",
                                        cpu, num_possible_cpus());
                                        break;
                                }
                                reboot_cpu = cpu;
                        } else
                                *mode = REBOOT_SOFT;
                        break;

                case 'g':
                        *mode = REBOOT_GPIO;
                        break;

                case 'b':
                case 'a':
                case 'k':
                case 't':
                case 'e':
                case 'p':
                        reboot_type = *str;
                        break;

                case 'f':
                        reboot_force = 1;
                        break;
                }

                str = strchr(str, ',');
                if (str)
                        str++;
                else
                        break;
        }
        return 1;
}
__setup("reboot=", reboot_setup);

#ifdef CONFIG_SYSFS

#define REBOOT_COLD_STR         "cold"
#define REBOOT_WARM_STR         "warm"
#define REBOOT_HARD_STR         "hard"
#define REBOOT_SOFT_STR         "soft"
#define REBOOT_GPIO_STR         "gpio"
#define REBOOT_UNDEFINED_STR    "undefined"

#define BOOT_TRIPLE_STR         "triple"
#define BOOT_KBD_STR            "kbd"
#define BOOT_BIOS_STR           "bios"
#define BOOT_ACPI_STR           "acpi"
#define BOOT_EFI_STR            "efi"
#define BOOT_PCI_STR            "pci"

static ssize_t mode_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        const char *val;

        switch (reboot_mode) {
        case REBOOT_COLD:
                val = REBOOT_COLD_STR;
                break;
        case REBOOT_WARM:
                val = REBOOT_WARM_STR;
                break;
        case REBOOT_HARD:
                val = REBOOT_HARD_STR;
                break;
        case REBOOT_SOFT:
                val = REBOOT_SOFT_STR;
                break;
        case REBOOT_GPIO:
                val = REBOOT_GPIO_STR;
                break;
        default:
                val = REBOOT_UNDEFINED_STR;
        }

        return sysfs_emit(buf, "%s\n", val);
}
static ssize_t mode_store(struct kobject *kobj, struct kobj_attribute *attr,
                          const char *buf, size_t count)
{
        if (!capable(CAP_SYS_BOOT))
                return -EPERM;

        if (!strncmp(buf, REBOOT_COLD_STR, strlen(REBOOT_COLD_STR)))
                reboot_mode = REBOOT_COLD;
        else if (!strncmp(buf, REBOOT_WARM_STR, strlen(REBOOT_WARM_STR)))
                reboot_mode = REBOOT_WARM;
        else if (!strncmp(buf, REBOOT_HARD_STR, strlen(REBOOT_HARD_STR)))
                reboot_mode = REBOOT_HARD;
        else if (!strncmp(buf, REBOOT_SOFT_STR, strlen(REBOOT_SOFT_STR)))
                reboot_mode = REBOOT_SOFT;
        else if (!strncmp(buf, REBOOT_GPIO_STR, strlen(REBOOT_GPIO_STR)))
                reboot_mode = REBOOT_GPIO;
        else
                return -EINVAL;

        reboot_default = 0;

        return count;
}
static struct kobj_attribute reboot_mode_attr = __ATTR_RW(mode);

#ifdef CONFIG_X86
static ssize_t force_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        return sysfs_emit(buf, "%d\n", reboot_force);
}
static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
                          const char *buf, size_t count)
{
        bool res;

        if (!capable(CAP_SYS_BOOT))
                return -EPERM;

        if (kstrtobool(buf, &res))
                return -EINVAL;

        reboot_default = 0;
        reboot_force = res;

        return count;
}
static struct kobj_attribute reboot_force_attr = __ATTR_RW(force);

static ssize_t type_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        const char *val;

        switch (reboot_type) {
        case BOOT_TRIPLE:
                val = BOOT_TRIPLE_STR;
                break;
        case BOOT_KBD:
                val = BOOT_KBD_STR;
                break;
        case BOOT_BIOS:
                val = BOOT_BIOS_STR;
                break;
        case BOOT_ACPI:
                val = BOOT_ACPI_STR;
                break;
        case BOOT_EFI:
                val = BOOT_EFI_STR;
                break;
        case BOOT_CF9_FORCE:
                val = BOOT_PCI_STR;
                break;
        default:
                val = REBOOT_UNDEFINED_STR;
        }

        return sysfs_emit(buf, "%s\n", val);
}
static ssize_t type_store(struct kobject *kobj, struct kobj_attribute *attr,
                          const char *buf, size_t count)
{
        if (!capable(CAP_SYS_BOOT))
                return -EPERM;

        if (!strncmp(buf, BOOT_TRIPLE_STR, strlen(BOOT_TRIPLE_STR)))
                reboot_type = BOOT_TRIPLE;
        else if (!strncmp(buf, BOOT_KBD_STR, strlen(BOOT_KBD_STR)))
                reboot_type = BOOT_KBD;
        else if (!strncmp(buf, BOOT_BIOS_STR, strlen(BOOT_BIOS_STR)))
                reboot_type = BOOT_BIOS;
        else if (!strncmp(buf, BOOT_ACPI_STR, strlen(BOOT_ACPI_STR)))
                reboot_type = BOOT_ACPI;
        else if (!strncmp(buf, BOOT_EFI_STR, strlen(BOOT_EFI_STR)))
                reboot_type = BOOT_EFI;
        else if (!strncmp(buf, BOOT_PCI_STR, strlen(BOOT_PCI_STR)))
                reboot_type = BOOT_CF9_FORCE;
        else
                return -EINVAL;

        reboot_default = 0;

        return count;
}
static struct kobj_attribute reboot_type_attr = __ATTR_RW(type);
#endif

#ifdef CONFIG_SMP
static ssize_t cpu_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        return sysfs_emit(buf, "%d\n", reboot_cpu);
}
static ssize_t cpu_store(struct kobject *kobj, struct kobj_attribute *attr,
                          const char *buf, size_t count)
{
        unsigned int cpunum;
        int rc;

        if (!capable(CAP_SYS_BOOT))
                return -EPERM;

        rc = kstrtouint(buf, 0, &cpunum);

        if (rc)
                return rc;

        if (cpunum >= num_possible_cpus())
                return -ERANGE;

        reboot_default = 0;
        reboot_cpu = cpunum;

        return count;
}
static struct kobj_attribute reboot_cpu_attr = __ATTR_RW(cpu);
#endif

static struct attribute *reboot_attrs[] = {
        &reboot_mode_attr.attr,
#ifdef CONFIG_X86
        &reboot_force_attr.attr,
        &reboot_type_attr.attr,
#endif
#ifdef CONFIG_SMP
        &reboot_cpu_attr.attr,
#endif
        NULL,
};

#ifdef CONFIG_SYSCTL
static struct ctl_table kern_reboot_table[] = {
        {
                .procname       = "poweroff_cmd",
                .data           = &poweroff_cmd,
                .maxlen         = POWEROFF_CMD_PATH_LEN,
                .mode           = 0644,
                .proc_handler   = proc_dostring,
        },
        {
                .procname       = "ctrl-alt-del",
                .data           = &C_A_D,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
};

static void __init kernel_reboot_sysctls_init(void)
{
        register_sysctl_init("kernel", kern_reboot_table);
}
#else
#define kernel_reboot_sysctls_init() do { } while (0)
#endif /* CONFIG_SYSCTL */

static const struct attribute_group reboot_attr_group = {
        .attrs = reboot_attrs,
};

static int __init reboot_ksysfs_init(void)
{
        struct kobject *reboot_kobj;
        int ret;

        reboot_kobj = kobject_create_and_add("reboot", kernel_kobj);
        if (!reboot_kobj)
                return -ENOMEM;

        ret = sysfs_create_group(reboot_kobj, &reboot_attr_group);
        if (ret) {
                kobject_put(reboot_kobj);
                return ret;
        }

        kernel_reboot_sysctls_init();

        return 0;
}
late_initcall(reboot_ksysfs_init);

#endif