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_KTHREAD)) 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 = current->state; 56 57 pr_debug("%s entered refrigerator\n", current->comm); 58 59 for (;;) { 60 set_current_state(TASK_UNINTERRUPTIBLE); 61 62 spin_lock_irq(&freezer_lock); 63 current->flags |= PF_FROZEN; 64 if (!freezing(current) || 65 (check_kthr_stop && kthread_should_stop())) 66 current->flags &= ~PF_FROZEN; 67 spin_unlock_irq(&freezer_lock); 68 69 if (!(current->flags & PF_FROZEN)) 70 break; 71 was_frozen = true; 72 schedule(); 73 } 74 75 pr_debug("%s left refrigerator\n", current->comm); 76 77 /* 78 * Restore saved task state before returning. The mb'd version 79 * needs to be used; otherwise, it might silently break 80 * synchronization which depends on ordered task state change. 81 */ 82 set_current_state(save); 83 84 return was_frozen; 85 } 86 EXPORT_SYMBOL(__refrigerator); 87 88 static void fake_signal_wake_up(struct task_struct *p) 89 { 90 unsigned long flags; 91 92 if (lock_task_sighand(p, &flags)) { 93 signal_wake_up(p, 0); 94 unlock_task_sighand(p, &flags); 95 } 96 } 97 98 /** 99 * freeze_task - send a freeze request to given task 100 * @p: task to send the request to 101 * 102 * If @p is freezing, the freeze request is sent by setting %TIF_FREEZE 103 * flag and either sending a fake signal to it or waking it up, depending 104 * on whether it has %PF_FREEZER_NOSIG set. 105 * 106 * RETURNS: 107 * %false, if @p is not freezing or already frozen; %true, otherwise 108 */ 109 bool freeze_task(struct task_struct *p) 110 { 111 unsigned long flags; 112 113 spin_lock_irqsave(&freezer_lock, flags); 114 if (!freezing(p) || frozen(p)) { 115 spin_unlock_irqrestore(&freezer_lock, flags); 116 return false; 117 } 118 119 if (!(p->flags & PF_KTHREAD)) { 120 fake_signal_wake_up(p); 121 /* 122 * fake_signal_wake_up() goes through p's scheduler 123 * lock and guarantees that TASK_STOPPED/TRACED -> 124 * TASK_RUNNING transition can't race with task state 125 * testing in try_to_freeze_tasks(). 126 */ 127 } else { 128 wake_up_state(p, TASK_INTERRUPTIBLE); 129 } 130 131 spin_unlock_irqrestore(&freezer_lock, flags); 132 return true; 133 } 134 135 void __thaw_task(struct task_struct *p) 136 { 137 unsigned long flags; 138 139 /* 140 * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to 141 * be visible to @p as waking up implies wmb. Waking up inside 142 * freezer_lock also prevents wakeups from leaking outside 143 * refrigerator. 144 */ 145 spin_lock_irqsave(&freezer_lock, flags); 146 if (frozen(p)) 147 wake_up_process(p); 148 spin_unlock_irqrestore(&freezer_lock, flags); 149 } 150 151 /** 152 * set_freezable - make %current freezable 153 * 154 * Mark %current freezable and enter refrigerator if necessary. 155 */ 156 bool set_freezable(void) 157 { 158 might_sleep(); 159 160 /* 161 * Modify flags while holding freezer_lock. This ensures the 162 * freezer notices that we aren't frozen yet or the freezing 163 * condition is visible to try_to_freeze() below. 164 */ 165 spin_lock_irq(&freezer_lock); 166 current->flags &= ~PF_NOFREEZE; 167 spin_unlock_irq(&freezer_lock); 168 169 return try_to_freeze(); 170 } 171 EXPORT_SYMBOL(set_freezable); 172