/*
 * drivers/power/process.c - Functions for starting/stopping processes on 
 *                           suspend transitions.
 *
 * Originally from swsusp.
 */


#undef DEBUG

#include <linux/interrupt.h>
#include <linux/oom.h>
#include <linux/suspend.h>
#include <linux/module.h>
#include <linux/sched/debug.h>
#include <linux/sched/task.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/delay.h>
#include <linux/workqueue.h>
#include <linux/kmod.h>
#include <trace/events/power.h>

/* 
 * Timeout for stopping processes
 */
unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;

static int try_to_freeze_tasks(bool user_only)
{
        struct task_struct *g, *p;
        unsigned long end_time;
        unsigned int todo;
        bool wq_busy = false;
        ktime_t start, end, elapsed;
        unsigned int elapsed_msecs;
        bool wakeup = false;
        int sleep_usecs = USEC_PER_MSEC;

        start = ktime_get_boottime();

        end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);

        if (!user_only)
                freeze_workqueues_begin();

        while (true) {
                todo = 0;
                read_lock(&tasklist_lock);
                for_each_process_thread(g, p) {
                        if (p == current || !freeze_task(p))
                                continue;

                        if (!freezer_should_skip(p))
                                todo++;
                }
                read_unlock(&tasklist_lock);

                if (!user_only) {
                        wq_busy = freeze_workqueues_busy();
                        todo += wq_busy;
                }

                if (!todo || time_after(jiffies, end_time))
                        break;

                if (pm_wakeup_pending()) {
                        wakeup = true;
                        break;
                }

                /*
                 * We need to retry, but first give the freezing tasks some
                 * time to enter the refrigerator.  Start with an initial
                 * 1 ms sleep followed by exponential backoff until 8 ms.
                 */
                usleep_range(sleep_usecs / 2, sleep_usecs);
                if (sleep_usecs < 8 * USEC_PER_MSEC)
                        sleep_usecs *= 2;
        }

        end = ktime_get_boottime();
        elapsed = ktime_sub(end, start);
        elapsed_msecs = ktime_to_ms(elapsed);

        if (todo) {
                pr_cont("\n");
                pr_err("Freezing of tasks %s after %d.%03d seconds "
                       "(%d tasks refusing to freeze, wq_busy=%d):\n",
                       wakeup ? "aborted" : "failed",
                       elapsed_msecs / 1000, elapsed_msecs % 1000,
                       todo - wq_busy, wq_busy);

                if (wq_busy)
                        show_workqueue_state();

                if (!wakeup) {
                        read_lock(&tasklist_lock);
                        for_each_process_thread(g, p) {
                                if (p != current && !freezer_should_skip(p)
                                    && freezing(p) && !frozen(p))
                                        sched_show_task(p);
                        }
                        read_unlock(&tasklist_lock);
                }
        } else {
                pr_cont("(elapsed %d.%03d seconds) ", elapsed_msecs / 1000,
                        elapsed_msecs % 1000);
        }

        return todo ? -EBUSY : 0;
}

/**
 * freeze_processes - Signal user space processes to enter the refrigerator.
 * The current thread will not be frozen.  The same process that calls
 * freeze_processes must later call thaw_processes.
 *
 * On success, returns 0.  On failure, -errno and system is fully thawed.
 */
int freeze_processes(void)
{
        int error;

        error = __usermodehelper_disable(UMH_FREEZING);
        if (error)
                return error;

        /* Make sure this task doesn't get frozen */
        current->flags |= PF_SUSPEND_TASK;

        if (!pm_freezing)
                atomic_inc(&system_freezing_cnt);

        pm_wakeup_clear(true);
        pr_info("Freezing user space processes ... ");
        pm_freezing = true;
        error = try_to_freeze_tasks(true);
        if (!error) {
                __usermodehelper_set_disable_depth(UMH_DISABLED);
                pr_cont("done.");
        }
        pr_cont("\n");
        BUG_ON(in_atomic());

        /*
         * Now that the whole userspace is frozen we need to disbale
         * the OOM killer to disallow any further interference with
         * killable tasks. There is no guarantee oom victims will
         * ever reach a point they go away we have to wait with a timeout.
         */
        if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs)))
                error = -EBUSY;

        if (error)
                thaw_processes();
        return error;
}

/**
 * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
 *
 * On success, returns 0.  On failure, -errno and only the kernel threads are
 * thawed, so as to give a chance to the caller to do additional cleanups
 * (if any) before thawing the userspace tasks. So, it is the responsibility
 * of the caller to thaw the userspace tasks, when the time is right.
 */
int freeze_kernel_threads(void)
{
        int error;

        pr_info("Freezing remaining freezable tasks ... ");

        pm_nosig_freezing = true;
        error = try_to_freeze_tasks(false);
        if (!error)
                pr_cont("done.");

        pr_cont("\n");
        BUG_ON(in_atomic());

        if (error)
                thaw_kernel_threads();
        return error;
}

void thaw_processes(void)
{
        struct task_struct *g, *p;
        struct task_struct *curr = current;

        trace_suspend_resume(TPS("thaw_processes"), 0, true);
        if (pm_freezing)
                atomic_dec(&system_freezing_cnt);
        pm_freezing = false;
        pm_nosig_freezing = false;

        oom_killer_enable();

        pr_info("Restarting tasks ... ");

        __usermodehelper_set_disable_depth(UMH_FREEZING);
        thaw_workqueues();

        read_lock(&tasklist_lock);
        for_each_process_thread(g, p) {
                /* No other threads should have PF_SUSPEND_TASK set */
                WARN_ON((p != curr) && (p->flags & PF_SUSPEND_TASK));
                __thaw_task(p);
        }
        read_unlock(&tasklist_lock);

        WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
        curr->flags &= ~PF_SUSPEND_TASK;

        usermodehelper_enable();

        schedule();
        pr_cont("done.\n");
        trace_suspend_resume(TPS("thaw_processes"), 0, false);
}

void thaw_kernel_threads(void)
{
        struct task_struct *g, *p;

        pm_nosig_freezing = false;
        pr_info("Restarting kernel threads ... ");

        thaw_workqueues();

        read_lock(&tasklist_lock);
        for_each_process_thread(g, p) {
                if (p->flags & (PF_KTHREAD | PF_WQ_WORKER))
                        __thaw_task(p);
        }
        read_unlock(&tasklist_lock);

        schedule();
        pr_cont("done.\n");
}