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 /* 23 * Temporary export for the deadlock workaround in ata_scsi_hotplug(). 24 * Remove once the hack becomes unnecessary. 25 */ 26 EXPORT_SYMBOL_GPL(pm_freezing); 27 28 /* protects freezing and frozen transitions */ 29 static DEFINE_SPINLOCK(freezer_lock); 30 31 /** 32 * freezing_slow_path - slow path for testing whether a task needs to be frozen 33 * @p: task to be tested 34 * 35 * This function is called by freezing() if system_freezing_cnt isn't zero 36 * and tests whether @p needs to enter and stay in frozen state. Can be 37 * called under any context. The freezers are responsible for ensuring the 38 * target tasks see the updated state. 39 */ 40 bool freezing_slow_path(struct task_struct *p) 41 { 42 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) 43 return false; 44 45 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 46 return false; 47 48 if (pm_nosig_freezing || cgroup_freezing(p)) 49 return true; 50 51 if (pm_freezing && !(p->flags & PF_KTHREAD)) 52 return true; 53 54 return false; 55 } 56 EXPORT_SYMBOL(freezing_slow_path); 57 58 /* Refrigerator is place where frozen processes are stored :-). */ 59 bool __refrigerator(bool check_kthr_stop) 60 { 61 /* Hmm, should we be allowed to suspend when there are realtime 62 processes around? */ 63 bool was_frozen = false; 64 long save = current->state; 65 66 pr_debug("%s entered refrigerator\n", current->comm); 67 68 for (;;) { 69 set_current_state(TASK_UNINTERRUPTIBLE); 70 71 spin_lock_irq(&freezer_lock); 72 current->flags |= PF_FROZEN; 73 if (!freezing(current) || 74 (check_kthr_stop && kthread_should_stop())) 75 current->flags &= ~PF_FROZEN; 76 spin_unlock_irq(&freezer_lock); 77 78 if (!(current->flags & PF_FROZEN)) 79 break; 80 was_frozen = true; 81 schedule(); 82 } 83 84 pr_debug("%s left refrigerator\n", current->comm); 85 86 /* 87 * Restore saved task state before returning. The mb'd version 88 * needs to be used; otherwise, it might silently break 89 * synchronization which depends on ordered task state change. 90 */ 91 set_current_state(save); 92 93 return was_frozen; 94 } 95 EXPORT_SYMBOL(__refrigerator); 96 97 static void fake_signal_wake_up(struct task_struct *p) 98 { 99 unsigned long flags; 100 101 if (lock_task_sighand(p, &flags)) { 102 signal_wake_up(p, 0); 103 unlock_task_sighand(p, &flags); 104 } 105 } 106 107 /** 108 * freeze_task - send a freeze request to given task 109 * @p: task to send the request to 110 * 111 * If @p is freezing, the freeze request is sent either by sending a fake 112 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 113 * thread). 114 * 115 * RETURNS: 116 * %false, if @p is not freezing or already frozen; %true, otherwise 117 */ 118 bool freeze_task(struct task_struct *p) 119 { 120 unsigned long flags; 121 122 /* 123 * This check can race with freezer_do_not_count, but worst case that 124 * will result in an extra wakeup being sent to the task. It does not 125 * race with freezer_count(), the barriers in freezer_count() and 126 * freezer_should_skip() ensure that either freezer_count() sees 127 * freezing == true in try_to_freeze() and freezes, or 128 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task 129 * normally. 130 */ 131 if (freezer_should_skip(p)) 132 return false; 133 134 spin_lock_irqsave(&freezer_lock, flags); 135 if (!freezing(p) || frozen(p)) { 136 spin_unlock_irqrestore(&freezer_lock, flags); 137 return false; 138 } 139 140 if (!(p->flags & PF_KTHREAD)) 141 fake_signal_wake_up(p); 142 else 143 wake_up_state(p, TASK_INTERRUPTIBLE); 144 145 spin_unlock_irqrestore(&freezer_lock, flags); 146 return true; 147 } 148 149 void __thaw_task(struct task_struct *p) 150 { 151 unsigned long flags; 152 153 spin_lock_irqsave(&freezer_lock, flags); 154 if (frozen(p)) 155 wake_up_process(p); 156 spin_unlock_irqrestore(&freezer_lock, flags); 157 } 158 159 /** 160 * set_freezable - make %current freezable 161 * 162 * Mark %current freezable and enter refrigerator if necessary. 163 */ 164 bool set_freezable(void) 165 { 166 might_sleep(); 167 168 /* 169 * Modify flags while holding freezer_lock. This ensures the 170 * freezer notices that we aren't frozen yet or the freezing 171 * condition is visible to try_to_freeze() below. 172 */ 173 spin_lock_irq(&freezer_lock); 174 current->flags &= ~PF_NOFREEZE; 175 spin_unlock_irq(&freezer_lock); 176 177 return try_to_freeze(); 178 } 179 EXPORT_SYMBOL(set_freezable); 180