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 = 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 spin_lock_irq(¤t->sighand->siglock); 76 recalc_sigpending(); /* We sent fake signal, clean it up */ 77 spin_unlock_irq(¤t->sighand->siglock); 78 79 pr_debug("%s left refrigerator\n", current->comm); 80 81 /* 82 * Restore saved task state before returning. The mb'd version 83 * needs to be used; otherwise, it might silently break 84 * synchronization which depends on ordered task state change. 85 */ 86 set_current_state(save); 87 88 return was_frozen; 89 } 90 EXPORT_SYMBOL(__refrigerator); 91 92 static void fake_signal_wake_up(struct task_struct *p) 93 { 94 unsigned long flags; 95 96 spin_lock_irqsave(&p->sighand->siglock, flags); 97 signal_wake_up(p, 0); 98 spin_unlock_irqrestore(&p->sighand->siglock, flags); 99 } 100 101 /** 102 * freeze_task - send a freeze request to given task 103 * @p: task to send the request to 104 * @sig_only: if set, the request will only be sent if the task has the 105 * PF_FREEZER_NOSIG flag unset 106 * Return value: 'false', if @sig_only is set and the task has 107 * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise 108 * 109 * The freeze request is sent by setting the tasks's TIF_FREEZE flag and 110 * either sending a fake signal to it or waking it up, depending on whether 111 * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task 112 * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its 113 * TIF_FREEZE flag will not be set. 114 */ 115 bool freeze_task(struct task_struct *p, bool sig_only) 116 { 117 unsigned long flags; 118 119 spin_lock_irqsave(&freezer_lock, flags); 120 if (!freezing(p) || frozen(p)) { 121 spin_unlock_irqrestore(&freezer_lock, flags); 122 return false; 123 } 124 125 if (!(p->flags & PF_FREEZER_NOSIG)) { 126 fake_signal_wake_up(p); 127 /* 128 * fake_signal_wake_up() goes through p's scheduler 129 * lock and guarantees that TASK_STOPPED/TRACED -> 130 * TASK_RUNNING transition can't race with task state 131 * testing in try_to_freeze_tasks(). 132 */ 133 } else { 134 wake_up_state(p, TASK_INTERRUPTIBLE); 135 } 136 137 spin_unlock_irqrestore(&freezer_lock, flags); 138 return true; 139 } 140 141 void __thaw_task(struct task_struct *p) 142 { 143 unsigned long flags; 144 145 /* 146 * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to 147 * be visible to @p as waking up implies wmb. Waking up inside 148 * freezer_lock also prevents wakeups from leaking outside 149 * refrigerator. 150 * 151 * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to 152 * avoid leaving dangling TIF_SIGPENDING behind. 153 */ 154 spin_lock_irqsave(&freezer_lock, flags); 155 if (frozen(p)) { 156 wake_up_process(p); 157 } else { 158 spin_lock(&p->sighand->siglock); 159 recalc_sigpending_and_wake(p); 160 spin_unlock(&p->sighand->siglock); 161 } 162 spin_unlock_irqrestore(&freezer_lock, flags); 163 } 164 165 /** 166 * __set_freezable - make %current freezable 167 * @with_signal: do we want %TIF_SIGPENDING for notification too? 168 * 169 * Mark %current freezable and enter refrigerator if necessary. 170 */ 171 bool __set_freezable(bool with_signal) 172 { 173 might_sleep(); 174 175 /* 176 * Modify flags while holding freezer_lock. This ensures the 177 * freezer notices that we aren't frozen yet or the freezing 178 * condition is visible to try_to_freeze() below. 179 */ 180 spin_lock_irq(&freezer_lock); 181 current->flags &= ~PF_NOFREEZE; 182 if (with_signal) 183 current->flags &= ~PF_FREEZER_NOSIG; 184 spin_unlock_irq(&freezer_lock); 185 186 return try_to_freeze(); 187 } 188 EXPORT_SYMBOL(__set_freezable); 189