PM: Handle device registrations during suspend/resume
Modify the PM core to protect its data structures, specifically the
dpm_active list, from being corrupted if a child of the currently
suspending device is registered concurrently with its ->suspend()
callback. In that case, since the new device (the child) is added
to dpm_active after its parent, the PM core will attempt to
suspend it after the parent, which is wrong.
Introduce a new member of struct dev_pm_info, called 'sleeping',
and use it to check if the parent of the device being added to
dpm_active has been suspended, in which case the device registration
fails. Also, use 'sleeping' for checking if the ordering of devices
on dpm_active is correct.
Introduce variable 'all_sleeping' that will be set to 'true' once all
devices have been suspended and make new device registrations fail
until 'all_sleeping' is reset to 'false', in order to avoid having
unsuspended devices around while the system is going into a sleep state.
Remove pm_sleep_rwsem which is not necessary any more.
Special thanks to Alan Stern for discussions and suggestions that
lead to the creation of this patch.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 461e4f1..421e7d0 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -196,6 +196,11 @@
The policy is that the device tree should match hardware bus topology.
(Or at least the control bus, for devices which use multiple busses.)
+In particular, this means that a device registration may fail if the parent of
+the device is suspending (ie. has been chosen by the PM core as the next
+device to suspend) or has already suspended, as well as after all of the other
+devices have been suspended. Device drivers must be prepared to cope with such
+situations.
Suspending Devices