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 set_current_state(TASK_FROZEN); 75 76 spin_lock_irq(&freezer_lock); 77 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop()); 78 spin_unlock_irq(&freezer_lock); 79 80 if (!freeze) 81 break; 82 83 was_frozen = true; 84 schedule(); 85 } 86 __set_current_state(TASK_RUNNING); 87 88 pr_debug("%s left refrigerator\n", current->comm); 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 static int __set_task_frozen(struct task_struct *p, void *arg) 105 { 106 unsigned int state = READ_ONCE(p->__state); 107 108 if (p->on_rq) 109 return 0; 110 111 if (p != current && task_curr(p)) 112 return 0; 113 114 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED))) 115 return 0; 116 117 /* 118 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they 119 * can suffer spurious wakeups. 120 */ 121 if (state & TASK_FREEZABLE) 122 WARN_ON_ONCE(!(state & TASK_NORMAL)); 123 124 #ifdef CONFIG_LOCKDEP 125 /* 126 * It's dangerous to freeze with locks held; there be dragons there. 127 */ 128 if (!(state & __TASK_FREEZABLE_UNSAFE)) 129 WARN_ON_ONCE(debug_locks && p->lockdep_depth); 130 #endif 131 132 WRITE_ONCE(p->__state, TASK_FROZEN); 133 return TASK_FROZEN; 134 } 135 136 static bool __freeze_task(struct task_struct *p) 137 { 138 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */ 139 return task_call_func(p, __set_task_frozen, NULL); 140 } 141 142 /** 143 * freeze_task - send a freeze request to given task 144 * @p: task to send the request to 145 * 146 * If @p is freezing, the freeze request is sent either by sending a fake 147 * signal (if it's not a kernel thread) or waking it up (if it's a kernel 148 * thread). 149 * 150 * RETURNS: 151 * %false, if @p is not freezing or already frozen; %true, otherwise 152 */ 153 bool freeze_task(struct task_struct *p) 154 { 155 unsigned long flags; 156 157 spin_lock_irqsave(&freezer_lock, flags); 158 if (!freezing(p) || frozen(p) || __freeze_task(p)) { 159 spin_unlock_irqrestore(&freezer_lock, flags); 160 return false; 161 } 162 163 if (!(p->flags & PF_KTHREAD)) 164 fake_signal_wake_up(p); 165 else 166 wake_up_state(p, TASK_NORMAL); 167 168 spin_unlock_irqrestore(&freezer_lock, flags); 169 return true; 170 } 171 172 /* 173 * The special task states (TASK_STOPPED, TASK_TRACED) keep their canonical 174 * state in p->jobctl. If either of them got a wakeup that was missed because 175 * TASK_FROZEN, then their canonical state reflects that and the below will 176 * refuse to restore the special state and instead issue the wakeup. 177 */ 178 static int __set_task_special(struct task_struct *p, void *arg) 179 { 180 unsigned int state = 0; 181 182 if (p->jobctl & JOBCTL_TRACED) 183 state = TASK_TRACED; 184 185 else if (p->jobctl & JOBCTL_STOPPED) 186 state = TASK_STOPPED; 187 188 if (state) 189 WRITE_ONCE(p->__state, state); 190 191 return state; 192 } 193 194 void __thaw_task(struct task_struct *p) 195 { 196 unsigned long flags, flags2; 197 198 spin_lock_irqsave(&freezer_lock, flags); 199 if (WARN_ON_ONCE(freezing(p))) 200 goto unlock; 201 202 if (lock_task_sighand(p, &flags2)) { 203 /* TASK_FROZEN -> TASK_{STOPPED,TRACED} */ 204 bool ret = task_call_func(p, __set_task_special, NULL); 205 unlock_task_sighand(p, &flags2); 206 if (ret) 207 goto unlock; 208 } 209 210 wake_up_state(p, TASK_FROZEN); 211 unlock: 212 spin_unlock_irqrestore(&freezer_lock, flags); 213 } 214 215 /** 216 * set_freezable - make %current freezable 217 * 218 * Mark %current freezable and enter refrigerator if necessary. 219 */ 220 bool set_freezable(void) 221 { 222 might_sleep(); 223 224 /* 225 * Modify flags while holding freezer_lock. This ensures the 226 * freezer notices that we aren't frozen yet or the freezing 227 * condition is visible to try_to_freeze() below. 228 */ 229 spin_lock_irq(&freezer_lock); 230 current->flags &= ~PF_NOFREEZE; 231 spin_unlock_irq(&freezer_lock); 232 233 return try_to_freeze(); 234 } 235 EXPORT_SYMBOL(set_freezable); 236