| 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); |