1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * kernel/freezer.c - Function to freeze a process 4 * 5 * Originally from kernel/power/process.c 6 */ 7 8 #include <linux/interrupt.h> 9 #include <linux/suspend.h> 10 #include <linux/export.h> 11 #include <linux/syscalls.h> 12 #include <linux/freezer.h> 13 #include <linux/kthread.h> 14 15 /* total number of freezing conditions in effect */ 16 atomic_t system_freezing_cnt = ATOMIC_INIT(0); 17 EXPORT_SYMBOL(system_freezing_cnt); 18 19 /* indicate whether PM freezing is in effect, protected by 20 * system_transition_mutex 21 */ 22 bool pm_freezing; 23 bool pm_nosig_freezing; 24 25 /* protects freezing and frozen transitions */ 26 static DEFINE_SPINLOCK(freezer_lock); 27 28 /** 29 * freezing_slow_path - slow path for testing whether a task needs to be frozen 30 * @p: task to be tested 31 * 32 * This function is called by freezing() if system_freezing_cnt isn't zero 33 * and tests whether @p needs to enter and stay in frozen state. Can be 34 * called under any context. The freezers are responsible for ensuring the 35 * target tasks see the updated state. 36 */ 37 bool freezing_slow_path(struct task_struct *p) 38 { 39 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) 40 return false; 41 42 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 43 return false; 44 45 if (pm_nosig_freezing || cgroup_freezing(p)) 46 return true; 47 48 if (pm_freezing && !(p->flags & PF_KTHREAD)) 49 return true; 50 51 return false; 52 } 53 EXPORT_SYMBOL(freezing_slow_path); 54 55 /* Refrigerator is place where frozen processes are stored :-). */ 56 bool __refrigerator(bool check_kthr_stop) 57 { 58 /* Hmm, should we be allowed to suspend when there are realtime 59 processes around? */ 60 bool was_frozen = false; 61 unsigned int save = get_current_state(); 62 63 pr_debug("%s entered refrigerator\n", current->comm); 64 65 for (;;) { 66 set_current_state(TASK_UNINTERRUPTIBLE); 67 68 spin_lock_irq(&freezer_lock); 69 current->flags |= PF_FROZEN; 70 if (!freezing(current) || 71 (check_kthr_stop && kthread_should_stop())) 72 current->flags &= ~PF_FROZEN; 73 spin_unlock_irq(&freezer_lock); 74 75 if (!(current->flags & PF_FROZEN)) 76 break; 77 was_frozen = true; 78 schedule(); 79 } 80 81 pr_debug("%s left refrigerator\n", current->comm); 82 83 /* 84 * Restore saved task state before returning. The mb'd version 85 * needs to be used; otherwise, it might silently break 86 * synchronization which depends on ordered task state change. 87 */ 88 set_current_state(save); 89 90 return was_frozen; 91 } 92 EXPORT_SYMBOL(__refrigerator); 93 94 static void fake_signal_wake_up(struct task_struct *p) 95 { 96 unsigned long flags; 97 98 if (lock_task_sighand(p, &flags)) { 99 signal_wake_up(p, 0); 100 unlock_task_sighand(p, &flags); 101 } 102 } 103 104 /** 105 * freeze_task - send a freeze request to given task 106 * @p: task to send the request to 107 * 108 * If @p is freezing, the freeze request is sent either by sending a fake 109 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 110 * thread). 111 * 112 * RETURNS: 113 * %false, if @p is not freezing or already frozen; %true, otherwise 114 */ 115 bool freeze_task(struct task_struct *p) 116 { 117 unsigned long flags; 118 119 /* 120 * This check can race with freezer_do_not_count, but worst case that 121 * will result in an extra wakeup being sent to the task. It does not 122 * race with freezer_count(), the barriers in freezer_count() and 123 * freezer_should_skip() ensure that either freezer_count() sees 124 * freezing == true in try_to_freeze() and freezes, or 125 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task 126 * normally. 127 */ 128 if (freezer_should_skip(p)) 129 return false; 130 131 spin_lock_irqsave(&freezer_lock, flags); 132 if (!freezing(p) || frozen(p)) { 133 spin_unlock_irqrestore(&freezer_lock, flags); 134 return false; 135 } 136 137 if (!(p->flags & PF_KTHREAD)) 138 fake_signal_wake_up(p); 139 else 140 wake_up_state(p, TASK_INTERRUPTIBLE); 141 142 spin_unlock_irqrestore(&freezer_lock, flags); 143 return true; 144 } 145 146 void __thaw_task(struct task_struct *p) 147 { 148 unsigned long flags; 149 150 spin_lock_irqsave(&freezer_lock, flags); 151 if (frozen(p)) 152 wake_up_process(p); 153 spin_unlock_irqrestore(&freezer_lock, flags); 154 } 155 156 /** 157 * set_freezable - make %current freezable 158 * 159 * Mark %current freezable and enter refrigerator if necessary. 160 */ 161 bool set_freezable(void) 162 { 163 might_sleep(); 164 165 /* 166 * Modify flags while holding freezer_lock. This ensures the 167 * freezer notices that we aren't frozen yet or the freezing 168 * condition is visible to try_to_freeze() below. 169 */ 170 spin_lock_irq(&freezer_lock); 171 current->flags &= ~PF_NOFREEZE; 172 spin_unlock_irq(&freezer_lock); 173 174 return try_to_freeze(); 175 } 176 EXPORT_SYMBOL(set_freezable); 177