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 /* 26 * Temporary export for the deadlock workaround in ata_scsi_hotplug(). 27 * Remove once the hack becomes unnecessary. 28 */ 29 EXPORT_SYMBOL_GPL(pm_freezing); 30 31 /* protects freezing and frozen transitions */ 32 static DEFINE_SPINLOCK(freezer_lock); 33 34 /** 35 * freezing_slow_path - slow path for testing whether a task needs to be frozen 36 * @p: task to be tested 37 * 38 * This function is called by freezing() if system_freezing_cnt isn't zero 39 * and tests whether @p needs to enter and stay in frozen state. Can be 40 * called under any context. The freezers are responsible for ensuring the 41 * target tasks see the updated state. 42 */ 43 bool freezing_slow_path(struct task_struct *p) 44 { 45 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) 46 return false; 47 48 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 49 return false; 50 51 if (pm_nosig_freezing || cgroup_freezing(p)) 52 return true; 53 54 if (pm_freezing && !(p->flags & PF_KTHREAD)) 55 return true; 56 57 return false; 58 } 59 EXPORT_SYMBOL(freezing_slow_path); 60 61 /* Refrigerator is place where frozen processes are stored :-). */ 62 bool __refrigerator(bool check_kthr_stop) 63 { 64 /* Hmm, should we be allowed to suspend when there are realtime 65 processes around? */ 66 bool was_frozen = false; 67 long save = current->state; 68 69 pr_debug("%s entered refrigerator\n", current->comm); 70 71 for (;;) { 72 set_current_state(TASK_UNINTERRUPTIBLE); 73 74 spin_lock_irq(&freezer_lock); 75 current->flags |= PF_FROZEN; 76 if (!freezing(current) || 77 (check_kthr_stop && kthread_should_stop())) 78 current->flags &= ~PF_FROZEN; 79 spin_unlock_irq(&freezer_lock); 80 81 if (!(current->flags & PF_FROZEN)) 82 break; 83 was_frozen = true; 84 schedule(); 85 } 86 87 pr_debug("%s left refrigerator\n", current->comm); 88 89 /* 90 * Restore saved task state before returning. The mb'd version 91 * needs to be used; otherwise, it might silently break 92 * synchronization which depends on ordered task state change. 93 */ 94 set_current_state(save); 95 96 return was_frozen; 97 } 98 EXPORT_SYMBOL(__refrigerator); 99 100 static void fake_signal_wake_up(struct task_struct *p) 101 { 102 unsigned long flags; 103 104 if (lock_task_sighand(p, &flags)) { 105 signal_wake_up(p, 0); 106 unlock_task_sighand(p, &flags); 107 } 108 } 109 110 /** 111 * freeze_task - send a freeze request to given task 112 * @p: task to send the request to 113 * 114 * If @p is freezing, the freeze request is sent either by sending a fake 115 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 116 * thread). 117 * 118 * RETURNS: 119 * %false, if @p is not freezing or already frozen; %true, otherwise 120 */ 121 bool freeze_task(struct task_struct *p) 122 { 123 unsigned long flags; 124 125 /* 126 * This check can race with freezer_do_not_count, but worst case that 127 * will result in an extra wakeup being sent to the task. It does not 128 * race with freezer_count(), the barriers in freezer_count() and 129 * freezer_should_skip() ensure that either freezer_count() sees 130 * freezing == true in try_to_freeze() and freezes, or 131 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task 132 * normally. 133 */ 134 if (freezer_should_skip(p)) 135 return false; 136 137 spin_lock_irqsave(&freezer_lock, flags); 138 if (!freezing(p) || frozen(p)) { 139 spin_unlock_irqrestore(&freezer_lock, flags); 140 return false; 141 } 142 143 if (!(p->flags & PF_KTHREAD)) 144 fake_signal_wake_up(p); 145 else 146 wake_up_state(p, TASK_INTERRUPTIBLE); 147 148 spin_unlock_irqrestore(&freezer_lock, flags); 149 return true; 150 } 151 152 void __thaw_task(struct task_struct *p) 153 { 154 unsigned long flags; 155 156 spin_lock_irqsave(&freezer_lock, flags); 157 if (frozen(p)) 158 wake_up_process(p); 159 spin_unlock_irqrestore(&freezer_lock, flags); 160 } 161 162 /** 163 * set_freezable - make %current freezable 164 * 165 * Mark %current freezable and enter refrigerator if necessary. 166 */ 167 bool set_freezable(void) 168 { 169 might_sleep(); 170 171 /* 172 * Modify flags while holding freezer_lock. This ensures the 173 * freezer notices that we aren't frozen yet or the freezing 174 * condition is visible to try_to_freeze() below. 175 */ 176 spin_lock_irq(&freezer_lock); 177 current->flags &= ~PF_NOFREEZE; 178 spin_unlock_irq(&freezer_lock); 179 180 return try_to_freeze(); 181 } 182 EXPORT_SYMBOL(set_freezable); 183