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 19 * system_transition_mutex 20 */ 21 bool pm_freezing; 22 bool pm_nosig_freezing; 23 24 /* 25 * Temporary export for the deadlock workaround in ata_scsi_hotplug(). 26 * Remove once the hack becomes unnecessary. 27 */ 28 EXPORT_SYMBOL_GPL(pm_freezing); 29 30 /* protects freezing and frozen transitions */ 31 static DEFINE_SPINLOCK(freezer_lock); 32 33 /** 34 * freezing_slow_path - slow path for testing whether a task needs to be frozen 35 * @p: task to be tested 36 * 37 * This function is called by freezing() if system_freezing_cnt isn't zero 38 * and tests whether @p needs to enter and stay in frozen state. Can be 39 * called under any context. The freezers are responsible for ensuring the 40 * target tasks see the updated state. 41 */ 42 bool freezing_slow_path(struct task_struct *p) 43 { 44 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) 45 return false; 46 47 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 48 return false; 49 50 if (pm_nosig_freezing || cgroup_freezing(p)) 51 return true; 52 53 if (pm_freezing && !(p->flags & PF_KTHREAD)) 54 return true; 55 56 return false; 57 } 58 EXPORT_SYMBOL(freezing_slow_path); 59 60 /* Refrigerator is place where frozen processes are stored :-). */ 61 bool __refrigerator(bool check_kthr_stop) 62 { 63 /* Hmm, should we be allowed to suspend when there are realtime 64 processes around? */ 65 bool was_frozen = false; 66 long save = current->state; 67 68 pr_debug("%s entered refrigerator\n", current->comm); 69 70 for (;;) { 71 set_current_state(TASK_UNINTERRUPTIBLE); 72 73 spin_lock_irq(&freezer_lock); 74 current->flags |= PF_FROZEN; 75 if (!freezing(current) || 76 (check_kthr_stop && kthread_should_stop())) 77 current->flags &= ~PF_FROZEN; 78 spin_unlock_irq(&freezer_lock); 79 80 if (!(current->flags & PF_FROZEN)) 81 break; 82 was_frozen = true; 83 schedule(); 84 } 85 86 pr_debug("%s left refrigerator\n", current->comm); 87 88 /* 89 * Restore saved task state before returning. The mb'd version 90 * needs to be used; otherwise, it might silently break 91 * synchronization which depends on ordered task state change. 92 */ 93 set_current_state(save); 94 95 return was_frozen; 96 } 97 EXPORT_SYMBOL(__refrigerator); 98 99 static void fake_signal_wake_up(struct task_struct *p) 100 { 101 unsigned long flags; 102 103 if (lock_task_sighand(p, &flags)) { 104 signal_wake_up(p, 0); 105 unlock_task_sighand(p, &flags); 106 } 107 } 108 109 /** 110 * freeze_task - send a freeze request to given task 111 * @p: task to send the request to 112 * 113 * If @p is freezing, the freeze request is sent either by sending a fake 114 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 115 * thread). 116 * 117 * RETURNS: 118 * %false, if @p is not freezing or already frozen; %true, otherwise 119 */ 120 bool freeze_task(struct task_struct *p) 121 { 122 unsigned long flags; 123 124 /* 125 * This check can race with freezer_do_not_count, but worst case that 126 * will result in an extra wakeup being sent to the task. It does not 127 * race with freezer_count(), the barriers in freezer_count() and 128 * freezer_should_skip() ensure that either freezer_count() sees 129 * freezing == true in try_to_freeze() and freezes, or 130 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task 131 * normally. 132 */ 133 if (freezer_should_skip(p)) 134 return false; 135 136 spin_lock_irqsave(&freezer_lock, flags); 137 if (!freezing(p) || frozen(p)) { 138 spin_unlock_irqrestore(&freezer_lock, flags); 139 return false; 140 } 141 142 if (!(p->flags & PF_KTHREAD)) 143 fake_signal_wake_up(p); 144 else 145 wake_up_state(p, TASK_INTERRUPTIBLE); 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 spin_lock_irqsave(&freezer_lock, flags); 156 if (frozen(p)) 157 wake_up_process(p); 158 spin_unlock_irqrestore(&freezer_lock, flags); 159 } 160 161 /** 162 * set_freezable - make %current freezable 163 * 164 * Mark %current freezable and enter refrigerator if necessary. 165 */ 166 bool set_freezable(void) 167 { 168 might_sleep(); 169 170 /* 171 * Modify flags while holding freezer_lock. This ensures the 172 * freezer notices that we aren't frozen yet or the freezing 173 * condition is visible to try_to_freeze() below. 174 */ 175 spin_lock_irq(&freezer_lock); 176 current->flags &= ~PF_NOFREEZE; 177 spin_unlock_irq(&freezer_lock); 178 179 return try_to_freeze(); 180 } 181 EXPORT_SYMBOL(set_freezable); 182