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 DEFINE_STATIC_KEY_FALSE(freezer_active); 17 EXPORT_SYMBOL(freezer_active); 18 19 /* 20 * indicate whether PM freezing is in effect, protected by 21 * system_transition_mutex 22 */ 23 bool pm_freezing; 24 bool pm_nosig_freezing; 25 26 /* protects freezing and frozen transitions */ 27 static DEFINE_SPINLOCK(freezer_lock); 28 29 /** 30 * freezing_slow_path - slow path for testing whether a task needs to be frozen 31 * @p: task to be tested 32 * 33 * This function is called by freezing() if freezer_active isn't zero 34 * and tests whether @p needs to enter and stay in frozen state. Can be 35 * called under any context. The freezers are responsible for ensuring the 36 * target tasks see the updated state. 37 */ 38 bool freezing_slow_path(struct task_struct *p) 39 { 40 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) 41 return false; 42 43 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 44 return false; 45 46 if (pm_nosig_freezing || cgroup_freezing(p)) 47 return true; 48 49 if (pm_freezing && !(p->flags & PF_KTHREAD)) 50 return true; 51 52 return false; 53 } 54 EXPORT_SYMBOL(freezing_slow_path); 55 56 bool frozen(struct task_struct *p) 57 { 58 return READ_ONCE(p->__state) & TASK_FROZEN; 59 } 60 61 /* Refrigerator is place where frozen processes are stored :-). */ 62 bool __refrigerator(bool check_kthr_stop) 63 { 64 unsigned int state = get_current_state(); 65 bool was_frozen = false; 66 67 pr_debug("%s entered refrigerator\n", current->comm); 68 69 WARN_ON_ONCE(state && !(state & TASK_NORMAL)); 70 71 for (;;) { 72 bool freeze; 73 74 raw_spin_lock_irq(¤t->pi_lock); 75 WRITE_ONCE(current->__state, TASK_FROZEN); 76 /* unstale saved_state so that __thaw_task() will wake us up */ 77 current->saved_state = TASK_RUNNING; 78 raw_spin_unlock_irq(¤t->pi_lock); 79 80 spin_lock_irq(&freezer_lock); 81 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop()); 82 spin_unlock_irq(&freezer_lock); 83 84 if (!freeze) 85 break; 86 87 was_frozen = true; 88 schedule(); 89 } 90 __set_current_state(TASK_RUNNING); 91 92 pr_debug("%s left refrigerator\n", current->comm); 93 94 return was_frozen; 95 } 96 EXPORT_SYMBOL(__refrigerator); 97 98 static void fake_signal_wake_up(struct task_struct *p) 99 { 100 unsigned long flags; 101 102 if (lock_task_sighand(p, &flags)) { 103 signal_wake_up(p, 0); 104 unlock_task_sighand(p, &flags); 105 } 106 } 107 108 static int __set_task_frozen(struct task_struct *p, void *arg) 109 { 110 unsigned int state = READ_ONCE(p->__state); 111 112 if (p->on_rq) 113 return 0; 114 115 if (p != current && task_curr(p)) 116 return 0; 117 118 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED))) 119 return 0; 120 121 /* 122 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they 123 * can suffer spurious wakeups. 124 */ 125 if (state & TASK_FREEZABLE) 126 WARN_ON_ONCE(!(state & TASK_NORMAL)); 127 128 #ifdef CONFIG_LOCKDEP 129 /* 130 * It's dangerous to freeze with locks held; there be dragons there. 131 */ 132 if (!(state & __TASK_FREEZABLE_UNSAFE)) 133 WARN_ON_ONCE(debug_locks && p->lockdep_depth); 134 #endif 135 136 p->saved_state = p->__state; 137 WRITE_ONCE(p->__state, TASK_FROZEN); 138 return TASK_FROZEN; 139 } 140 141 static bool __freeze_task(struct task_struct *p) 142 { 143 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */ 144 return task_call_func(p, __set_task_frozen, NULL); 145 } 146 147 /** 148 * freeze_task - send a freeze request to given task 149 * @p: task to send the request to 150 * 151 * If @p is freezing, the freeze request is sent either by sending a fake 152 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 153 * thread). 154 * 155 * RETURNS: 156 * %false, if @p is not freezing or already frozen; %true, otherwise 157 */ 158 bool freeze_task(struct task_struct *p) 159 { 160 unsigned long flags; 161 162 spin_lock_irqsave(&freezer_lock, flags); 163 if (!freezing(p) || frozen(p) || __freeze_task(p)) { 164 spin_unlock_irqrestore(&freezer_lock, flags); 165 return false; 166 } 167 168 if (!(p->flags & PF_KTHREAD)) 169 fake_signal_wake_up(p); 170 else 171 wake_up_state(p, TASK_NORMAL); 172 173 spin_unlock_irqrestore(&freezer_lock, flags); 174 return true; 175 } 176 177 /* 178 * Restore the saved_state before the task entered freezer. For typical task 179 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens 180 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state 181 * is restored unless they got an expected wakeup (see ttwu_state_match()). 182 * Returns 1 if the task state was restored. 183 */ 184 static int __restore_freezer_state(struct task_struct *p, void *arg) 185 { 186 unsigned int state = p->saved_state; 187 188 if (state != TASK_RUNNING) { 189 WRITE_ONCE(p->__state, state); 190 p->saved_state = TASK_RUNNING; 191 return 1; 192 } 193 194 return 0; 195 } 196 197 void __thaw_task(struct task_struct *p) 198 { 199 unsigned long flags; 200 201 spin_lock_irqsave(&freezer_lock, flags); 202 if (WARN_ON_ONCE(freezing(p))) 203 goto unlock; 204 205 if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL)) 206 goto unlock; 207 208 wake_up_state(p, TASK_FROZEN); 209 unlock: 210 spin_unlock_irqrestore(&freezer_lock, flags); 211 } 212 213 /** 214 * set_freezable - make %current freezable 215 * 216 * Mark %current freezable and enter refrigerator if necessary. 217 */ 218 bool set_freezable(void) 219 { 220 might_sleep(); 221 222 /* 223 * Modify flags while holding freezer_lock. This ensures the 224 * freezer notices that we aren't frozen yet or the freezing 225 * condition is visible to try_to_freeze() below. 226 */ 227 spin_lock_irq(&freezer_lock); 228 current->flags &= ~PF_NOFREEZE; 229 spin_unlock_irq(&freezer_lock); 230 231 return try_to_freeze(); 232 } 233 EXPORT_SYMBOL(set_freezable); 234