提交 9045a050 编写于 作者: S Srivatsa S. Bhat 提交者: Rafael J. Wysocki

PM / Freezer / Docs: Document the beauty of freeze/thaw semantics

The way the different freeze/thaw functions encapsulate each other are quite
lovely from a design point of view. And as a side-effect, the way in which
they are invoked (cleaning up on failure for example) differs significantly
from how usual functions are dealt with. This is because of the underlying
semantics that govern the freezing and thawing of various tasks.

This subtle aspect that differentiates these functions from the rest, is
worth documenting.

Many thanks to Tejun Heo for providing enlightenment on this topic.
Signed-off-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
上级 8916e370
......@@ -63,6 +63,27 @@ devices have been reinitialized, the function thaw_processes() is called in
order to clear the PF_FROZEN flag for each frozen task. Then, the tasks that
have been frozen leave __refrigerator() and continue running.
Rationale behind the functions dealing with freezing and thawing of tasks:
-------------------------------------------------------------------------
freeze_processes():
- freezes only userspace tasks
freeze_kernel_threads():
- freezes all tasks (including kernel threads) because we can't freeze
kernel threads without freezing userspace tasks
thaw_kernel_threads():
- thaws only kernel threads; this is particularly useful if we need to do
anything special in between thawing of kernel threads and thawing of
userspace tasks, or if we want to postpone the thawing of userspace tasks
thaw_processes():
- thaws all tasks (including kernel threads) because we can't thaw userspace
tasks without thawing kernel threads
III. Which kernel threads are freezable?
Kernel threads are not freezable by default. However, a kernel thread may clear
......
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