PM: Do not hold dpm_list_mtx while disabling/enabling nonboot CPUs

We shouldn't hold dpm_list_mtx while executing
[disable|enable]_nonboot_cpus(), because theoretically this may lead
to a deadlock as shown by the following example (provided by Johannes
Berg):

CPU 3       CPU 2                     CPU 1
                                      suspend/hibernate
            something:
            rtnl_lock()               device_pm_lock()
                                       -> mutex_lock(&dpm_list_mtx)

            mutex_lock(&dpm_list_mtx)

linkwatch_work
 -> rtnl_lock()
                                      disable_nonboot_cpus()
                                       -> flush CPU 3 workqueue

Fortunately, device drivers are supposed to stop any activities that
might lead to the registration of new device objects way before
disable_nonboot_cpus() is called, so it shouldn't be necessary to
hold dpm_list_mtx over the entire late part of device suspend and
early part of device resume.

Thus, during the late suspend and the early resume of devices acquire
dpm_list_mtx only when dpm_list is going to be traversed and release
it right after that.

This patch is reported to fix the regressions tracked as
http://bugzilla.kernel.org/show_bug.cgi?id=13245.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Miles Lane <miles.lane@gmail.com>
Tested-by: Ming Lei <tom.leiming@gmail.com>

1 files changed, 1 insertions, 6 deletions

diff --git a/kernel/power/main.c b/kernel/power/main.c
index f99ed6a75eac..868028280d13 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -289,12 +289,10 @@ static int suspend_enter(suspend_state_t state)
 {
 	int error;
 
-	device_pm_lock();
-
 	if (suspend_ops->prepare) {
 		error = suspend_ops->prepare();
 		if (error)
-			goto Done;
+			return error;
 	}
 
 	error = device_power_down(PMSG_SUSPEND);
@@ -343,9 +341,6 @@ static int suspend_enter(suspend_state_t state)
 	if (suspend_ops->finish)
 		suspend_ops->finish();
 
- Done:
-	device_pm_unlock();
-
 	return error;
 }