process.c

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/*
 * 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/syscalls.h>
#include <linux/freezer.h>
#include <linux/delay.h>
#include <linux/workqueue.h>
#include <linux/kmod.h>

/* 
 * Timeout for stopping processes
 */
#define TIMEOUT (20 * HZ)

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;
    struct timeval start, end;
    u64 elapsed_csecs64;
    unsigned int elapsed_csecs;
    bool wakeup = false;

    do_gettimeofday(&start);

    end_time = jiffies + TIMEOUT;

    if (!user_only)
        freeze_workqueues_begin();

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

            /*
             * Now that we've done set_freeze_flag, don't
             * perturb a task in TASK_STOPPED or TASK_TRACED.
             * It is "frozen enough".  If the task does wake
             * up, it will immediately call try_to_freeze.
             *
             * Because freeze_task() goes through p's scheduler lock, it's
             * guaranteed that TASK_STOPPED/TRACED -> TASK_RUNNING
             * transition can't race with task state testing here.
             */
            if (!task_is_stopped_or_traced(p) &&
                !freezer_should_skip(p))
                todo++;
        } while_each_thread(g, p);
        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.
         */
        msleep(10);
    }

    do_gettimeofday(&end);
    elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);
    do_div(elapsed_csecs64, NSEC_PER_SEC / 100);
    elapsed_csecs = elapsed_csecs64;

    if (todo) {
        printk("\n");
        printk(KERN_ERR "Freezing of tasks %s after %d.%02d seconds "
               "(%d tasks refusing to freeze, wq_busy=%d):\n",
               wakeup ? "aborted" : "failed",
               elapsed_csecs / 100, elapsed_csecs % 100,
               todo - wq_busy, wq_busy);

        if (!wakeup) {
            read_lock(&tasklist_lock);
            do_each_thread(g, p) {
                if (p != current && !freezer_should_skip(p)
                    && freezing(p) && !frozen(p))
                    sched_show_task(p);
            } while_each_thread(g, p);
            read_unlock(&tasklist_lock);
        }
    } else {
        printk("(elapsed %d.%02d seconds) ", elapsed_csecs / 100,
            elapsed_csecs % 100);
    }

    return todo ? -EBUSY : 0;
}

int freeze_processes(void)
{
    int error;

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

    if (!pm_freezing)
        atomic_inc(&system_freezing_cnt);

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

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

int freeze_kernel_threads(void)
{
    int error;

    printk("Freezing remaining freezable tasks ... ");
    pm_nosig_freezing = true;
    error = try_to_freeze_tasks(false);
    if (!error)
        printk("done.");

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

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

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

    if (pm_freezing)
        atomic_dec(&system_freezing_cnt);
    pm_freezing = false;
    pm_nosig_freezing = false;

    oom_killer_enable();

    printk("Restarting tasks ... ");

    thaw_workqueues();

    read_lock(&tasklist_lock);
    do_each_thread(g, p) {
        __thaw_task(p);
    } while_each_thread(g, p);
    read_unlock(&tasklist_lock);

    usermodehelper_enable();

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

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

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

    thaw_workqueues();

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

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