FreeBSD/Linux Kernel Cross Reference
sys/kernel/freezer.c

     /*
      * kernel/freezer.c - Function to freeze a process
      *
      * Originally from kernel/power/process.c
      */
     
     #include <linux/interrupt.h>
     #include <linux/suspend.h>
     #include <linux/export.h>
    #include <linux/syscalls.h>
    #include <linux/freezer.h>
    #include <linux/kthread.h>
    
    /* total number of freezing conditions in effect */
    atomic_t system_freezing_cnt = ATOMIC_INIT(0);
    EXPORT_SYMBOL(system_freezing_cnt);
    
    /* indicate whether PM freezing is in effect, protected by pm_mutex */
    bool pm_freezing;
    bool pm_nosig_freezing;
    
    /* protects freezing and frozen transitions */
    static DEFINE_SPINLOCK(freezer_lock);
    
    /**
     * freezing_slow_path - slow path for testing whether a task needs to be frozen
     * @p: task to be tested
     *
     * This function is called by freezing() if system_freezing_cnt isn't zero
     * and tests whether @p needs to enter and stay in frozen state.  Can be
     * called under any context.  The freezers are responsible for ensuring the
     * target tasks see the updated state.
     */
    bool freezing_slow_path(struct task_struct *p)
    {
            if (p->flags & PF_NOFREEZE)
                    return false;
    
            if (pm_nosig_freezing || cgroup_freezing(p))
                    return true;
    
            if (pm_freezing && !(p->flags & PF_KTHREAD))
                    return true;
    
            return false;
    }
    EXPORT_SYMBOL(freezing_slow_path);
    
    /* Refrigerator is place where frozen processes are stored :-). */
    bool __refrigerator(bool check_kthr_stop)
    {
            /* Hmm, should we be allowed to suspend when there are realtime
               processes around? */
            bool was_frozen = false;
            long save = current->state;
    
            pr_debug("%s entered refrigerator\n", current->comm);
    
            for (;;) {
                    set_current_state(TASK_UNINTERRUPTIBLE);
    
                    spin_lock_irq(&freezer_lock);
                    current->flags |= PF_FROZEN;
                    if (!freezing(current) ||
                        (check_kthr_stop && kthread_should_stop()))
                            current->flags &= ~PF_FROZEN;
                    spin_unlock_irq(&freezer_lock);
    
                    if (!(current->flags & PF_FROZEN))
                            break;
                    was_frozen = true;
                    schedule();
            }
    
            pr_debug("%s left refrigerator\n", current->comm);
    
            /*
             * Restore saved task state before returning.  The mb'd version
             * needs to be used; otherwise, it might silently break
             * synchronization which depends on ordered task state change.
             */
            set_current_state(save);
    
            return was_frozen;
    }
    EXPORT_SYMBOL(__refrigerator);
    
    static void fake_signal_wake_up(struct task_struct *p)
    {
            unsigned long flags;
    
            if (lock_task_sighand(p, &flags)) {
                    signal_wake_up(p, 0);
                    unlock_task_sighand(p, &flags);
            }
    }
    
    /**
     * freeze_task - send a freeze request to given task
    * @p: task to send the request to
    *
    * If @p is freezing, the freeze request is sent either by sending a fake
    * signal (if it's not a kernel thread) or waking it up (if it's a kernel
    * thread).
    *
    * RETURNS:
    * %false, if @p is not freezing or already frozen; %true, otherwise
    */
   bool freeze_task(struct task_struct *p)
   {
           unsigned long flags;
   
           spin_lock_irqsave(&freezer_lock, flags);
           if (!freezing(p) || frozen(p)) {
                   spin_unlock_irqrestore(&freezer_lock, flags);
                   return false;
           }
   
           if (!(p->flags & PF_KTHREAD))
                   fake_signal_wake_up(p);
           else
                   wake_up_state(p, TASK_INTERRUPTIBLE);
   
           spin_unlock_irqrestore(&freezer_lock, flags);
           return true;
   }
   
   void __thaw_task(struct task_struct *p)
   {
           unsigned long flags;
   
           /*
            * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
            * be visible to @p as waking up implies wmb.  Waking up inside
            * freezer_lock also prevents wakeups from leaking outside
            * refrigerator.
            */
           spin_lock_irqsave(&freezer_lock, flags);
           if (frozen(p))
                   wake_up_process(p);
           spin_unlock_irqrestore(&freezer_lock, flags);
   }
   
   /**
    * set_freezable - make %current freezable
    *
    * Mark %current freezable and enter refrigerator if necessary.
    */
   bool set_freezable(void)
   {
           might_sleep();
   
           /*
            * Modify flags while holding freezer_lock.  This ensures the
            * freezer notices that we aren't frozen yet or the freezing
            * condition is visible to try_to_freeze() below.
            */
           spin_lock_irq(&freezer_lock);
           current->flags &= ~PF_NOFREEZE;
           spin_unlock_irq(&freezer_lock);
   
           return try_to_freeze();
   }
   EXPORT_SYMBOL(set_freezable);

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