Documentation/power/freezing-of-tasks.rst

11 kernel threads are controlled during hibernation or system-wide suspend (on some
17 There is one per-task flag (PF_NOFREEZE) and three per-task states
21 system enters a sleep state as well as before a hibernation image is created
23 to system-wide suspend too).
26 freeze_processes() (defined in kernel/power/process.c) is called.  A system-wide
27 static key freezer_active (as opposed to a per-task flag or state) is used to
28 indicate whether the system is to undergo a freezing operation. And
45 signal-handling code, but the freezable kernel threads need to call it
61 			oom_reaper_list = tsk->oom_reaper_list;
73 entire system-wide transition will be cancelled.  For this reason, freezable
77 After the system memory state has been restored from a hibernation image and
84 -------------------------------------------------------------------------
87   - freezes only userspace tasks
90   - freezes all tasks (including kernel threads) because we can't freeze
94   - thaws only kernel threads; this is particularly useful if we need to do
99   - thaws all tasks (including kernel threads) because we can't thaw userspace
122    filesystem-related information that must be consistent with the state of the
123    on-disk data and metadata after the system memory state has been restored
126    tasks that might cause the on-disk filesystems' data and metadata to be
128    system is finally powered off. The majority of these are user space
148 … on LKML (https://lore.kernel.org/r/alpine.LFD.0.98.0704271801020.9964@woody.linux-foundation.org):
173    space processes should not notice that such a system-wide operation has
200    (https://lists.linux-foundation.org/pipermail/linux-pm/2007-May/012309.html).
222 Documentation/driver-api/pm/notifiers.rst.
230 piece of code from system-wide sleep such as suspend/hibernation is not
233 CPU-Hotplug code (kernel/cpu.c) for an example.