kernel/power/process.c

   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 #include <linux/interrupt.h>
  10 #include <linux/oom.h>
  11 #include <linux/suspend.h>
  12 #include <linux/module.h>
  13 #include <linux/sched/debug.h>
  14 #include <linux/sched/task.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/freezer.h>
  17 #include <linux/delay.h>
  18 #include <linux/workqueue.h>
  19 #include <linux/kmod.h>
  20 #include <trace/events/power.h>
  21 #include <linux/cpuset.h>
  22
  23 /*
  24  * Timeout for stopping processes
  25  */
  26 unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
  27
  28 static int try_to_freeze_tasks(bool user_only)
  29 {
  30         const char *what = user_only ? "user space processes" :
  31                                         "remaining freezable tasks";
  32         struct task_struct *g, *p;
  33         unsigned long end_time;
  34         unsigned int todo;
  35         bool wq_busy = false;
  36         ktime_t start, end, elapsed;
  37         unsigned int elapsed_msecs;
  38         bool wakeup = false;
  39         int sleep_usecs = USEC_PER_MSEC;
  40
  41         pr_info("Freezing %s\n", what);
  42
  43         start = ktime_get_boottime();
  44
  45         end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
  46
  47         if (!user_only)
  48                 freeze_workqueues_begin();
  49
  50         while (true) {
  51                 todo = 0;
  52                 read_lock(&tasklist_lock);
  53                 for_each_process_thread(g, p) {
  54                         if (p == current || !freeze_task(p))
  55                                 continue;
  56
  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_err("Freezing %s %s after %d.%03d seconds "
  90                        "(%d tasks refusing to freeze, wq_busy=%d):\n", what,
  91                        wakeup ? "aborted" : "failed",
  92                        elapsed_msecs / 1000, elapsed_msecs % 1000,
  93                        todo - wq_busy, wq_busy);
  94
  95                 if (wq_busy)
  96                         show_freezable_workqueues();
  97
  98                 if (!wakeup || pm_debug_messages_on) {
  99                         read_lock(&tasklist_lock);
 100                         for_each_process_thread(g, p) {
 101                                 if (p != current && freezing(p) && !frozen(p))
 102                                         sched_show_task(p);
 103                         }
 104                         read_unlock(&tasklist_lock);
 105                 }
 106         } else {
 107                 pr_info("Freezing %s completed (elapsed %d.%03d seconds)\n",
 108                         what, elapsed_msecs / 1000, elapsed_msecs % 1000);
 109         }
 110
 111         return todo ? -EBUSY : 0;
 112 }
 113
 114 /**
 115  * freeze_processes - Signal user space processes to enter the refrigerator.
 116  * The current thread will not be frozen.  The same process that calls
 117  * freeze_processes must later call thaw_processes.
 118  *
 119  * On success, returns 0.  On failure, -errno and system is fully thawed.
 120  */
 121 int freeze_processes(void)
 122 {
 123         int error;
 124
 125         error = __usermodehelper_disable(UMH_FREEZING);
 126         if (error)
 127                 return error;
 128
 129         /* Make sure this task doesn't get frozen */
 130         current->flags |= PF_SUSPEND_TASK;
 131
 132         if (!pm_freezing)
 133                 static_branch_inc(&freezer_active);
 134
 135         pm_wakeup_clear(0);
 136         pm_freezing = true;
 137         error = try_to_freeze_tasks(true);
 138         if (!error)
 139                 __usermodehelper_set_disable_depth(UMH_DISABLED);
 140
 141         BUG_ON(in_atomic());
 142
 143         /*
 144          * Now that the whole userspace is frozen we need to disable
 145          * the OOM killer to disallow any further interference with
 146          * killable tasks. There is no guarantee oom victims will
 147          * ever reach a point they go away we have to wait with a timeout.
 148          */
 149         if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs)))
 150                 error = -EBUSY;
 151
 152         if (error)
 153                 thaw_processes();
 154         return error;
 155 }
 156
 157 /**
 158  * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
 159  *
 160  * On success, returns 0.  On failure, -errno and only the kernel threads are
 161  * thawed, so as to give a chance to the caller to do additional cleanups
 162  * (if any) before thawing the userspace tasks. So, it is the responsibility
 163  * of the caller to thaw the userspace tasks, when the time is right.
 164  */
 165 int freeze_kernel_threads(void)
 166 {
 167         int error;
 168
 169         pm_nosig_freezing = true;
 170         error = try_to_freeze_tasks(false);
 171
 172         BUG_ON(in_atomic());
 173
 174         if (error)
 175                 thaw_kernel_threads();
 176         return error;
 177 }
 178
 179 void thaw_processes(void)
 180 {
 181         struct task_struct *g, *p;
 182         struct task_struct *curr = current;
 183
 184         trace_suspend_resume(TPS("thaw_processes"), 0, true);
 185         if (pm_freezing)
 186                 static_branch_dec(&freezer_active);
 187         pm_freezing = false;
 188         pm_nosig_freezing = false;
 189
 190         oom_killer_enable();
 191
 192         pr_info("Restarting tasks ... ");
 193
 194         __usermodehelper_set_disable_depth(UMH_FREEZING);
 195         thaw_workqueues();
 196
 197         cpuset_wait_for_hotplug();
 198
 199         read_lock(&tasklist_lock);
 200         for_each_process_thread(g, p) {
 201                 /* No other threads should have PF_SUSPEND_TASK set */
 202                 WARN_ON((p != curr) && (p->flags & PF_SUSPEND_TASK));
 203                 __thaw_task(p);
 204         }
 205         read_unlock(&tasklist_lock);
 206
 207         WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
 208         curr->flags &= ~PF_SUSPEND_TASK;
 209
 210         usermodehelper_enable();
 211
 212         schedule();
 213         pr_cont("done.\n");
 214         trace_suspend_resume(TPS("thaw_processes"), 0, false);
 215 }
 216
 217 void thaw_kernel_threads(void)
 218 {
 219         struct task_struct *g, *p;
 220
 221         pm_nosig_freezing = false;
 222         pr_info("Restarting kernel threads ... ");
 223
 224         thaw_workqueues();
 225
 226         read_lock(&tasklist_lock);
 227         for_each_process_thread(g, p) {
 228                 if (p->flags & PF_KTHREAD)
 229                         __thaw_task(p);
 230         }
 231         read_unlock(&tasklist_lock);
 232
 233         schedule();
 234         pr_cont("done.\n");
 235 }