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 /* 113 * Allow freezing the sched_delayed tasks; they will not execute until 114 * ttwu() fixes them up, so it is safe to swap their state now, instead 115 * of waiting for them to get fully dequeued. 116 */ 117 if (task_is_runnable(p)) 118 return 0; 119 120 if (p != current && task_curr(p)) 121 return 0; 122 123 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED))) 124 return 0; 125 126 /* 127 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they 128 * can suffer spurious wakeups. 129 */ 130 if (state & TASK_FREEZABLE) 131 WARN_ON_ONCE(!(state & TASK_NORMAL)); 132 133 #ifdef CONFIG_LOCKDEP 134 /* 135 * It's dangerous to freeze with locks held; there be dragons there. 136 */ 137 if (!(state & __TASK_FREEZABLE_UNSAFE)) 138 WARN_ON_ONCE(debug_locks && p->lockdep_depth); 139 #endif 140 141 p->saved_state = p->__state; 142 WRITE_ONCE(p->__state, TASK_FROZEN); 143 return TASK_FROZEN; 144 } 145 146 static bool __freeze_task(struct task_struct *p) 147 { 148 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */ 149 return task_call_func(p, __set_task_frozen, NULL); 150 } 151 152 /** 153 * freeze_task - send a freeze request to given task 154 * @p: task to send the request to 155 * 156 * If @p is freezing, the freeze request is sent either by sending a fake 157 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 158 * thread). 159 * 160 * RETURNS: 161 * %false, if @p is not freezing or already frozen; %true, otherwise 162 */ 163 bool freeze_task(struct task_struct *p) 164 { 165 unsigned long flags; 166 167 spin_lock_irqsave(&freezer_lock, flags); 168 if (!freezing(p) || frozen(p) || __freeze_task(p)) { 169 spin_unlock_irqrestore(&freezer_lock, flags); 170 return false; 171 } 172 173 if (!(p->flags & PF_KTHREAD)) 174 fake_signal_wake_up(p); 175 else 176 wake_up_state(p, TASK_NORMAL); 177 178 spin_unlock_irqrestore(&freezer_lock, flags); 179 return true; 180 } 181 182 /* 183 * Restore the saved_state before the task entered freezer. For typical task 184 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens 185 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state 186 * is restored unless they got an expected wakeup (see ttwu_state_match()). 187 * Returns 1 if the task state was restored. 188 */ 189 static int __restore_freezer_state(struct task_struct *p, void *arg) 190 { 191 unsigned int state = p->saved_state; 192 193 if (state != TASK_RUNNING) { 194 WRITE_ONCE(p->__state, state); 195 p->saved_state = TASK_RUNNING; 196 return 1; 197 } 198 199 return 0; 200 } 201 202 void __thaw_task(struct task_struct *p) 203 { 204 unsigned long flags; 205 206 spin_lock_irqsave(&freezer_lock, flags); 207 if (WARN_ON_ONCE(freezing(p))) 208 goto unlock; 209 210 if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL)) 211 goto unlock; 212 213 wake_up_state(p, TASK_FROZEN); 214 unlock: 215 spin_unlock_irqrestore(&freezer_lock, flags); 216 } 217 218 /** 219 * set_freezable - make %current freezable 220 * 221 * Mark %current freezable and enter refrigerator if necessary. 222 */ 223 bool set_freezable(void) 224 { 225 might_sleep(); 226 227 /* 228 * Modify flags while holding freezer_lock. This ensures the 229 * freezer notices that we aren't frozen yet or the freezing 230 * condition is visible to try_to_freeze() below. 231 */ 232 spin_lock_irq(&freezer_lock); 233 current->flags &= ~PF_NOFREEZE; 234 spin_unlock_irq(&freezer_lock); 235 236 return try_to_freeze(); 237 } 238 EXPORT_SYMBOL(set_freezable); 239