/* * 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); /* * fake_signal_wake_up() goes through p's scheduler * lock and guarantees that TASK_STOPPED/TRACED -> * TASK_RUNNING transition can't race with task state * testing in try_to_freeze_tasks(). */ } 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);