root/kernel/power/process.c

DEFINITIONS

1. try_to_freeze_tasks
2. freeze_processes
3. freeze_kernel_threads
4. thaw_processes
5. thaw_kernel_threads

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * drivers/power/process.c - Functions for starting/stopping processes on 
   4  *                           suspend transitions.
   5  *
   6  * Originally from swsusp.
   7  */
   8 
   9 
  10 #undef DEBUG
  11 
  12 #include <linux/interrupt.h>
  13 #include <linux/oom.h>
  14 #include <linux/suspend.h>
  15 #include <linux/module.h>
  16 #include <linux/sched/debug.h>
  17 #include <linux/sched/task.h>
  18 #include <linux/syscalls.h>
  19 #include <linux/freezer.h>
  20 #include <linux/delay.h>
  21 #include <linux/workqueue.h>
  22 #include <linux/kmod.h>
  23 #include <trace/events/power.h>
  24 #include <linux/cpuset.h>
  25 
  26 /*
  27  * Timeout for stopping processes
  28  */
  29 unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
  30 
  31 static int try_to_freeze_tasks(bool user_only)
  32 {
  33         struct task_struct *g, *p;
  34         unsigned long end_time;
  35         unsigned int todo;
  36         bool wq_busy = false;
  37         ktime_t start, end, elapsed;
  38         unsigned int elapsed_msecs;
  39         bool wakeup = false;
  40         int sleep_usecs = USEC_PER_MSEC;
  41 
  42         start = ktime_get_boottime();
  43 
  44         end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
  45 
  46         if (!user_only)
  47                 freeze_workqueues_begin();
  48 
  49         while (true) {
  50                 todo = 0;
  51                 read_lock(&tasklist_lock);
  52                 for_each_process_thread(g, p) {
  53                         if (p == current || !freeze_task(p))
  54                                 continue;
  55 
  56                         if (!freezer_should_skip(p))
  57                                 todo++;
  58                 }
  59                 read_unlock(&tasklist_lock);
  60 
  61                 if (!user_only) {
  62                         wq_busy = freeze_workqueues_busy();
  63                         todo += wq_busy;
  64                 }
  65 
  66                 if (!todo || time_after(jiffies, end_time))
  67                         break;
  68 
  69                 if (pm_wakeup_pending()) {
  70                         wakeup = true;
  71                         break;
  72                 }
  73 
  74                 /*
  75                  * We need to retry, but first give the freezing tasks some
  76                  * time to enter the refrigerator.  Start with an initial
  77                  * 1 ms sleep followed by exponential backoff until 8 ms.
  78                  */
  79                 usleep_range(sleep_usecs / 2, sleep_usecs);
  80                 if (sleep_usecs < 8 * USEC_PER_MSEC)
  81                         sleep_usecs *= 2;
  82         }
  83 
  84         end = ktime_get_boottime();
  85         elapsed = ktime_sub(end, start);
  86         elapsed_msecs = ktime_to_ms(elapsed);
  87 
  88         if (todo) {
  89                 pr_cont("\n");
  90                 pr_err("Freezing of tasks %s after %d.%03d seconds "
  91                        "(%d tasks refusing to freeze, wq_busy=%d):\n",
  92                        wakeup ? "aborted" : "failed",
  93                        elapsed_msecs / 1000, elapsed_msecs % 1000,
  94                        todo - wq_busy, wq_busy);
  95 
  96                 if (wq_busy)
  97                         show_workqueue_state();
  98 
  99                 if (!wakeup || pm_debug_messages_on) {
 100                         read_lock(&tasklist_lock);
 101                         for_each_process_thread(g, p) {
 102                                 if (p != current && !freezer_should_skip(p)
 103                                     && freezing(p) && !frozen(p))
 104                                         sched_show_task(p);
 105                         }
 106                         read_unlock(&tasklist_lock);
 107                 }
 108         } else {
 109                 pr_cont("(elapsed %d.%03d seconds) ", elapsed_msecs / 1000,
 110                         elapsed_msecs % 1000);
 111         }
 112 
 113         return todo ? -EBUSY : 0;
 114 }
 115 
 116 /**
 117  * freeze_processes - Signal user space processes to enter the refrigerator.
 118  * The current thread will not be frozen.  The same process that calls
 119  * freeze_processes must later call thaw_processes.
 120  *
 121  * On success, returns 0.  On failure, -errno and system is fully thawed.
 122  */
 123 int freeze_processes(void)
 124 {
 125         int error;
 126 
 127         error = __usermodehelper_disable(UMH_FREEZING);
 128         if (error)
 129                 return error;
 130 
 131         /* Make sure this task doesn't get frozen */
 132         current->flags |= PF_SUSPEND_TASK;
 133 
 134         if (!pm_freezing)
 135                 atomic_inc(&system_freezing_cnt);
 136 
 137         pm_wakeup_clear(true);
 138         pr_info("Freezing user space processes ... ");
 139         pm_freezing = true;
 140         error = try_to_freeze_tasks(true);
 141         if (!error) {
 142                 __usermodehelper_set_disable_depth(UMH_DISABLED);
 143                 pr_cont("done.");
 144         }
 145         pr_cont("\n");
 146         BUG_ON(in_atomic());
 147 
 148         /*
 149          * Now that the whole userspace is frozen we need to disbale
 150          * the OOM killer to disallow any further interference with
 151          * killable tasks. There is no guarantee oom victims will
 152          * ever reach a point they go away we have to wait with a timeout.
 153          */
 154         if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs)))
 155                 error = -EBUSY;
 156 
 157         if (error)
 158                 thaw_processes();
 159         return error;
 160 }
 161 
 162 /**
 163  * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
 164  *
 165  * On success, returns 0.  On failure, -errno and only the kernel threads are
 166  * thawed, so as to give a chance to the caller to do additional cleanups
 167  * (if any) before thawing the userspace tasks. So, it is the responsibility
 168  * of the caller to thaw the userspace tasks, when the time is right.
 169  */
 170 int freeze_kernel_threads(void)
 171 {
 172         int error;
 173 
 174         pr_info("Freezing remaining freezable tasks ... ");
 175 
 176         pm_nosig_freezing = true;
 177         error = try_to_freeze_tasks(false);
 178         if (!error)
 179                 pr_cont("done.");
 180 
 181         pr_cont("\n");
 182         BUG_ON(in_atomic());
 183 
 184         if (error)
 185                 thaw_kernel_threads();
 186         return error;
 187 }
 188 
 189 void thaw_processes(void)
 190 {
 191         struct task_struct *g, *p;
 192         struct task_struct *curr = current;
 193 
 194         trace_suspend_resume(TPS("thaw_processes"), 0, true);
 195         if (pm_freezing)
 196                 atomic_dec(&system_freezing_cnt);
 197         pm_freezing = false;
 198         pm_nosig_freezing = false;
 199 
 200         oom_killer_enable();
 201 
 202         pr_info("Restarting tasks ... ");
 203 
 204         __usermodehelper_set_disable_depth(UMH_FREEZING);
 205         thaw_workqueues();
 206 
 207         cpuset_wait_for_hotplug();
 208 
 209         read_lock(&tasklist_lock);
 210         for_each_process_thread(g, p) {
 211                 /* No other threads should have PF_SUSPEND_TASK set */
 212                 WARN_ON((p != curr) && (p->flags & PF_SUSPEND_TASK));
 213                 __thaw_task(p);
 214         }
 215         read_unlock(&tasklist_lock);
 216 
 217         WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
 218         curr->flags &= ~PF_SUSPEND_TASK;
 219 
 220         usermodehelper_enable();
 221 
 222         schedule();
 223         pr_cont("done.\n");
 224         trace_suspend_resume(TPS("thaw_processes"), 0, false);
 225 }
 226 
 227 void thaw_kernel_threads(void)
 228 {
 229         struct task_struct *g, *p;
 230 
 231         pm_nosig_freezing = false;
 232         pr_info("Restarting kernel threads ... ");
 233 
 234         thaw_workqueues();
 235 
 236         read_lock(&tasklist_lock);
 237         for_each_process_thread(g, p) {
 238                 if (p->flags & (PF_KTHREAD | PF_WQ_WORKER))
 239                         __thaw_task(p);
 240         }
 241         read_unlock(&tasklist_lock);
 242 
 243         schedule();
 244         pr_cont("done.\n");
 245 }