LCOV - code coverage report
Current view: top level - kernel - freezer.c (source / functions) Hit Total Coverage
Test: combined.info Lines: 6 56 10.7 %
Date: 2022-04-01 14:58:12 Functions: 1 6 16.7 %
Branches: 0 32 0.0 %

           Branch data     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                 :          0 :                 return true;
      47                 :            : 
      48   [ #  #  #  # ]:          0 :         if (pm_freezing && !(p->flags & PF_KTHREAD))
      49                 :          0 :                 return true;
      50                 :            : 
      51                 :            :         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 :         long save = current->state;
      62                 :            : 
      63                 :          0 :         pr_debug("%s entered refrigerator\n", current->comm);
      64                 :            : 
      65                 :          0 :         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                 :          0 :         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                 :          0 :         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                 :          0 :         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                 :          0 :         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                 :         15 : bool set_freezable(void)
     162                 :            : {
     163                 :         15 :         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                 :         15 :         spin_lock_irq(&freezer_lock);
     171                 :         15 :         current->flags &= ~PF_NOFREEZE;
     172                 :         15 :         spin_unlock_irq(&freezer_lock);
     173                 :            : 
     174                 :         15 :         return try_to_freeze();
     175                 :            : }
     176                 :            : EXPORT_SYMBOL(set_freezable);

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