1 /* 2 * kernel/freezer.c - Function to freeze a process 3 * 4 * Originally from kernel/power/process.c 5 */ 6 7 #include <linux/interrupt.h> 8 #include <linux/suspend.h> 9 #include <linux/export.h> 10 #include <linux/syscalls.h> 11 #include <linux/freezer.h> 12 #include <linux/kthread.h> 13 14 /* total number of freezing conditions in effect */ 15 atomic_t system_freezing_cnt = ATOMIC_INIT(0); 16 EXPORT_SYMBOL(system_freezing_cnt); 17 18 /* indicate whether PM freezing is in effect, protected by pm_mutex */ 19 bool pm_freezing; 20 bool pm_nosig_freezing; 21 22 /* protects freezing and frozen transitions */ 23 static DEFINE_SPINLOCK(freezer_lock); 24 25 /** 26 * freezing_slow_path - slow path for testing whether a task needs to be frozen 27 * @p: task to be tested 28 * 29 * This function is called by freezing() if system_freezing_cnt isn't zero 30 * and tests whether @p needs to enter and stay in frozen state. Can be 31 * called under any context. The freezers are responsible for ensuring the 32 * target tasks see the updated state. 33 */ 34 bool freezing_slow_path(struct task_struct *p) 35 { 36 if (p->flags & PF_NOFREEZE) 37 return false; 38 39 if (pm_nosig_freezing || cgroup_freezing(p)) 40 return true; 41 42 if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG)) 43 return true; 44 45 return false; 46 } 47 EXPORT_SYMBOL(freezing_slow_path); 48 49 /* Refrigerator is place where frozen processes are stored :-). */ 50 bool __refrigerator(bool check_kthr_stop) 51 { 52 /* Hmm, should we be allowed to suspend when there are realtime 53 processes around? */ 54 bool was_frozen = false; 55 long save; 56 57 /* 58 * No point in checking freezing() again - the caller already did. 59 * Proceed to enter FROZEN. 60 */ 61 spin_lock_irq(&freezer_lock); 62 repeat: 63 current->flags |= PF_FROZEN; 64 spin_unlock_irq(&freezer_lock); 65 66 save = current->state; 67 pr_debug("%s entered refrigerator\n", current->comm); 68 69 spin_lock_irq(¤t->sighand->siglock); 70 recalc_sigpending(); /* We sent fake signal, clean it up */ 71 spin_unlock_irq(¤t->sighand->siglock); 72 73 for (;;) { 74 set_current_state(TASK_UNINTERRUPTIBLE); 75 if (!freezing(current) || 76 (check_kthr_stop && kthread_should_stop())) 77 break; 78 was_frozen = true; 79 schedule(); 80 } 81 82 /* leave FROZEN */ 83 spin_lock_irq(&freezer_lock); 84 if (freezing(current)) 85 goto repeat; 86 current->flags &= ~PF_FROZEN; 87 spin_unlock_irq(&freezer_lock); 88 89 pr_debug("%s left refrigerator\n", current->comm); 90 91 /* 92 * Restore saved task state before returning. The mb'd version 93 * needs to be used; otherwise, it might silently break 94 * synchronization which depends on ordered task state change. 95 */ 96 set_current_state(save); 97 98 return was_frozen; 99 } 100 EXPORT_SYMBOL(__refrigerator); 101 102 static void fake_signal_wake_up(struct task_struct *p) 103 { 104 unsigned long flags; 105 106 spin_lock_irqsave(&p->sighand->siglock, flags); 107 signal_wake_up(p, 0); 108 spin_unlock_irqrestore(&p->sighand->siglock, flags); 109 } 110 111 /** 112 * freeze_task - send a freeze request to given task 113 * @p: task to send the request to 114 * @sig_only: if set, the request will only be sent if the task has the 115 * PF_FREEZER_NOSIG flag unset 116 * Return value: 'false', if @sig_only is set and the task has 117 * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise 118 * 119 * The freeze request is sent by setting the tasks's TIF_FREEZE flag and 120 * either sending a fake signal to it or waking it up, depending on whether 121 * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task 122 * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its 123 * TIF_FREEZE flag will not be set. 124 */ 125 bool freeze_task(struct task_struct *p, bool sig_only) 126 { 127 unsigned long flags; 128 129 spin_lock_irqsave(&freezer_lock, flags); 130 if (!freezing(p) || frozen(p)) { 131 spin_unlock_irqrestore(&freezer_lock, flags); 132 return false; 133 } 134 135 if (should_send_signal(p)) { 136 fake_signal_wake_up(p); 137 /* 138 * fake_signal_wake_up() goes through p's scheduler 139 * lock and guarantees that TASK_STOPPED/TRACED -> 140 * TASK_RUNNING transition can't race with task state 141 * testing in try_to_freeze_tasks(). 142 */ 143 } else { 144 wake_up_state(p, TASK_INTERRUPTIBLE); 145 } 146 147 spin_unlock_irqrestore(&freezer_lock, flags); 148 return true; 149 } 150 151 void __thaw_task(struct task_struct *p) 152 { 153 unsigned long flags; 154 155 /* 156 * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to 157 * be visible to @p as waking up implies wmb. Waking up inside 158 * freezer_lock also prevents wakeups from leaking outside 159 * refrigerator. 160 * 161 * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to 162 * avoid leaving dangling TIF_SIGPENDING behind. 163 */ 164 spin_lock_irqsave(&freezer_lock, flags); 165 if (frozen(p)) { 166 wake_up_process(p); 167 } else { 168 spin_lock(&p->sighand->siglock); 169 recalc_sigpending_and_wake(p); 170 spin_unlock(&p->sighand->siglock); 171 } 172 spin_unlock_irqrestore(&freezer_lock, flags); 173 } 174