/* * kernel/freezer.c - Function to freeze a process * * Originally from kernel/power/process.c */ #include <linux/interrupt.h> #include <linux/suspend.h> #include <linux/module.h> #include <linux/syscalls.h> #include <linux/freezer.h> /* * freezing is complete, mark current process as frozen */ static inline void frozen_process(void) { if (!unlikely(current->flags & PF_NOFREEZE)) { current->flags |= PF_FROZEN; smp_wmb(); } clear_freeze_flag(current); } /* Refrigerator is place where frozen processes are stored :-). */ void refrigerator(void) { /* Hmm, should we be allowed to suspend when there are realtime processes around? */ long save; task_lock(current); if (freezing(current)) { frozen_process(); task_unlock(current); } else { task_unlock(current); return; } save = current->state; pr_debug("%s entered refrigerator\n", current->comm); spin_lock_irq(¤t->sighand->siglock); recalc_sigpending(); /* We sent fake signal, clean it up */ spin_unlock_irq(¤t->sighand->siglock); /* prevent accounting of that task to load */ current->flags |= PF_FREEZING; for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); if (!frozen(current)) break; schedule(); } /* Remove the accounting blocker */ current->flags &= ~PF_FREEZING; pr_debug("%s left refrigerator\n", current->comm); __set_current_state(save); } EXPORT_SYMBOL(refrigerator); static void fake_signal_wake_up(struct task_struct *p) { unsigned long flags; spin_lock_irqsave(&p->sighand->siglock, flags); signal_wake_up(p, 0); spin_unlock_irqrestore(&p->sighand->siglock, flags); } /** * freeze_task - send a freeze request to given task * @p: task to send the request to * @sig_only: if set, the request will only be sent if the task has the * PF_FREEZER_NOSIG flag unset * Return value: 'false', if @sig_only is set and the task has * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise * * The freeze request is sent by setting the tasks's TIF_FREEZE flag and * either sending a fake signal to it or waking it up, depending on whether * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its * TIF_FREEZE flag will not be set. */ bool freeze_task(struct task_struct *p, bool sig_only) { /* * We first check if the task is freezing and next if it has already * been frozen to avoid the race with frozen_process() which first marks * the task as frozen and next clears its TIF_FREEZE. */ if (!freezing(p)) { smp_rmb(); if (frozen(p)) return false; if (!sig_only || should_send_signal(p)) set_freeze_flag(p); else return false; } if (should_send_signal(p)) { 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 if (sig_only) { return false; } else { wake_up_state(p, TASK_INTERRUPTIBLE); } return true; } void cancel_freezing(struct task_struct *p) { unsigned long flags; if (freezing(p)) { pr_debug(" clean up: %s\n", p->comm); clear_freeze_flag(p); spin_lock_irqsave(&p->sighand->siglock, flags); recalc_sigpending_and_wake(p); spin_unlock_irqrestore(&p->sighand->siglock, flags); } } static int __thaw_process(struct task_struct *p) { if (frozen(p)) { p->flags &= ~PF_FROZEN; return 1; } clear_freeze_flag(p); return 0; } /* * Wake up a frozen process * * task_lock() is needed to prevent the race with refrigerator() which may * occur if the freezing of tasks fails. Namely, without the lock, if the * freezing of tasks failed, thaw_tasks() might have run before a task in * refrigerator() could call frozen_process(), in which case the task would be * frozen and no one would thaw it. */ int thaw_process(struct task_struct *p) { task_lock(p); if (__thaw_process(p) == 1) { task_unlock(p); wake_up_process(p); return 1; } task_unlock(p); return 0; } EXPORT_SYMBOL(thaw_process);