Line data    Source code

       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             : /* protects freezing and frozen transitions */
      26             : static DEFINE_SPINLOCK(freezer_lock);
      27             : 
      28             : /**
      29             :  * freezing_slow_path - slow path for testing whether a task needs to be frozen
      30             :  * @p: task to be tested
      31             :  *
      32             :  * This function is called by freezing() if system_freezing_cnt isn't zero
      33             :  * and tests whether @p needs to enter and stay in frozen state.  Can be
      34             :  * called under any context.  The freezers are responsible for ensuring the
      35             :  * target tasks see the updated state.
      36             :  */
      37           0 : bool freezing_slow_path(struct task_struct *p)
      38             : {
      39           0 :         if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
      40             :                 return false;
      41             : 
      42           0 :         if (test_tsk_thread_flag(p, TIF_MEMDIE))
      43             :                 return false;
      44             : 
      45           0 :         if (pm_nosig_freezing || cgroup_freezing(p))
      46             :                 return true;
      47             : 
      48           0 :         if (pm_freezing && !(p->flags & PF_KTHREAD))
      49             :                 return true;
      50             : 
      51           0 :         return false;
      52             : }
      53             : EXPORT_SYMBOL(freezing_slow_path);
      54             : 
      55             : /* Refrigerator is place where frozen processes are stored :-). */
      56           0 : bool __refrigerator(bool check_kthr_stop)
      57             : {
      58             :         /* Hmm, should we be allowed to suspend when there are realtime
      59             :            processes around? */
      60           0 :         bool was_frozen = false;
      61           0 :         unsigned int save = get_current_state();
      62             : 
      63             :         pr_debug("%s entered refrigerator\n", current->comm);
      64             : 
      65             :         for (;;) {
      66           0 :                 set_current_state(TASK_UNINTERRUPTIBLE);
      67             : 
      68           0 :                 spin_lock_irq(&freezer_lock);
      69           0 :                 current->flags |= PF_FROZEN;
      70           0 :                 if (!freezing(current) ||
      71           0 :                     (check_kthr_stop && kthread_should_stop()))
      72           0 :                         current->flags &= ~PF_FROZEN;
      73           0 :                 spin_unlock_irq(&freezer_lock);
      74             : 
      75           0 :                 if (!(current->flags & PF_FROZEN))
      76             :                         break;
      77           0 :                 was_frozen = true;
      78           0 :                 schedule();
      79             :         }
      80             : 
      81             :         pr_debug("%s left refrigerator\n", current->comm);
      82             : 
      83             :         /*
      84             :          * Restore saved task state before returning.  The mb'd version
      85             :          * needs to be used; otherwise, it might silently break
      86             :          * synchronization which depends on ordered task state change.
      87             :          */
      88           0 :         set_current_state(save);
      89             : 
      90           0 :         return was_frozen;
      91             : }
      92             : EXPORT_SYMBOL(__refrigerator);
      93             : 
      94           0 : static void fake_signal_wake_up(struct task_struct *p)
      95             : {
      96             :         unsigned long flags;
      97             : 
      98           0 :         if (lock_task_sighand(p, &flags)) {
      99           0 :                 signal_wake_up(p, 0);
     100           0 :                 unlock_task_sighand(p, &flags);
     101             :         }
     102           0 : }
     103             : 
     104             : /**
     105             :  * freeze_task - send a freeze request to given task
     106             :  * @p: task to send the request to
     107             :  *
     108             :  * If @p is freezing, the freeze request is sent either by sending a fake
     109             :  * signal (if it's not a kernel thread) or waking it up (if it's a kernel
     110             :  * thread).
     111             :  *
     112             :  * RETURNS:
     113             :  * %false, if @p is not freezing or already frozen; %true, otherwise
     114             :  */
     115           0 : bool freeze_task(struct task_struct *p)
     116             : {
     117             :         unsigned long flags;
     118             : 
     119             :         /*
     120             :          * This check can race with freezer_do_not_count, but worst case that
     121             :          * will result in an extra wakeup being sent to the task.  It does not
     122             :          * race with freezer_count(), the barriers in freezer_count() and
     123             :          * freezer_should_skip() ensure that either freezer_count() sees
     124             :          * freezing == true in try_to_freeze() and freezes, or
     125             :          * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
     126             :          * normally.
     127             :          */
     128           0 :         if (freezer_should_skip(p))
     129             :                 return false;
     130             : 
     131           0 :         spin_lock_irqsave(&freezer_lock, flags);
     132           0 :         if (!freezing(p) || frozen(p)) {
     133           0 :                 spin_unlock_irqrestore(&freezer_lock, flags);
     134           0 :                 return false;
     135             :         }
     136             : 
     137           0 :         if (!(p->flags & PF_KTHREAD))
     138           0 :                 fake_signal_wake_up(p);
     139             :         else
     140           0 :                 wake_up_state(p, TASK_INTERRUPTIBLE);
     141             : 
     142           0 :         spin_unlock_irqrestore(&freezer_lock, flags);
     143           0 :         return true;
     144             : }
     145             : 
     146           0 : void __thaw_task(struct task_struct *p)
     147             : {
     148             :         unsigned long flags;
     149             : 
     150           0 :         spin_lock_irqsave(&freezer_lock, flags);
     151           0 :         if (frozen(p))
     152           0 :                 wake_up_process(p);
     153           0 :         spin_unlock_irqrestore(&freezer_lock, flags);
     154           0 : }
     155             : 
     156             : /**
     157             :  * set_freezable - make %current freezable
     158             :  *
     159             :  * Mark %current freezable and enter refrigerator if necessary.
     160             :  */
     161           3 : bool set_freezable(void)
     162             : {
     163             :         might_sleep();
     164             : 
     165             :         /*
     166             :          * Modify flags while holding freezer_lock.  This ensures the
     167             :          * freezer notices that we aren't frozen yet or the freezing
     168             :          * condition is visible to try_to_freeze() below.
     169             :          */
     170           3 :         spin_lock_irq(&freezer_lock);
     171           3 :         current->flags &= ~PF_NOFREEZE;
     172           3 :         spin_unlock_irq(&freezer_lock);
     173             : 
     174           3 :         return try_to_freeze();
     175             : }
     176             : EXPORT_SYMBOL(set_freezable);