Commit 82586a72 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

PM: runtime: Avoid device usage count underflows 



A PM-runtime device usage count underflow is potentially critical,
because it may cause a device to be suspended when it is expected to
be operational.  It is also a programming problem that would be good
to catch and warn about.

For this reason, (1) make rpm_check_suspend_allowed() return an error
when the device usage count is negative to prevent devices from being
suspended in that case, (2) introduce rpm_drop_usage_count() that will
detect device usage count underflows, warn about them and fix them up,
and (3) use it to drop the usage count in a few places instead of
atomic_dec_and_test().

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
parent bd8284e9

drivers/base/power/runtime.c

+37 −7
Original line number Diff line number Diff line
@@ -263,7 +263,7 @@ static int rpm_check_suspend_allowed(struct device *dev) 
		retval = -EINVAL;

	else if (dev->power.disable_depth > 0)

		retval = -EACCES;

	else if (atomic_read(&dev->power.usage_count) > 0)

	else if (atomic_read(&dev->power.usage_count))

		retval = -EAGAIN;

	else if (!dev->power.ignore_children &&

			atomic_read(&dev->power.child_count))
@@ -1039,13 +1039,33 @@ int pm_schedule_suspend(struct device *dev, unsigned int delay) 
}

EXPORT_SYMBOL_GPL(pm_schedule_suspend);



static int rpm_drop_usage_count(struct device *dev)

{

	int ret;



	ret = atomic_sub_return(1, &dev->power.usage_count);

	if (ret >= 0)

		return ret;



	/*

	 * Because rpm_resume() does not check the usage counter, it will resume

	 * the device even if the usage counter is 0 or negative, so it is

	 * sufficient to increment the usage counter here to reverse the change

	 * made above.

	 */

	atomic_inc(&dev->power.usage_count);

	dev_warn(dev, "Runtime PM usage count underflow!\n");

	return -EINVAL;

}



/**

 * __pm_runtime_idle - Entry point for runtime idle operations.

 * @dev: Device to send idle notification for.

 * @rpmflags: Flag bits.

 *

 * If the RPM_GET_PUT flag is set, decrement the device's usage count and

 * return immediately if it is larger than zero.  Then carry out an idle

 * return immediately if it is larger than zero (if it becomes negative, log a

 * warning, increment it, and return an error).  Then carry out an idle

 * notification, either synchronous or asynchronous.

 *

 * This routine may be called in atomic context if the RPM_ASYNC flag is set,
@@ -1057,7 +1077,10 @@ int __pm_runtime_idle(struct device *dev, int rpmflags) 
	int retval;



	if (rpmflags & RPM_GET_PUT) {

		if (!atomic_dec_and_test(&dev->power.usage_count)) {

		retval = rpm_drop_usage_count(dev);

		if (retval < 0) {

			return retval;

		} else if (retval > 0) {

			trace_rpm_usage_rcuidle(dev, rpmflags);

			return 0;

		}
@@ -1079,7 +1102,8 @@ EXPORT_SYMBOL_GPL(__pm_runtime_idle); 
 * @rpmflags: Flag bits.

 *

 * If the RPM_GET_PUT flag is set, decrement the device's usage count and

 * return immediately if it is larger than zero.  Then carry out a suspend,

 * return immediately if it is larger than zero (if it becomes negative, log a

 * warning, increment it, and return an error).  Then carry out a suspend,

 * either synchronous or asynchronous.

 *

 * This routine may be called in atomic context if the RPM_ASYNC flag is set,
@@ -1091,7 +1115,10 @@ int __pm_runtime_suspend(struct device *dev, int rpmflags) 
	int retval;



	if (rpmflags & RPM_GET_PUT) {

		if (!atomic_dec_and_test(&dev->power.usage_count)) {

		retval = rpm_drop_usage_count(dev);

		if (retval < 0) {

			return retval;

		} else if (retval > 0) {

			trace_rpm_usage_rcuidle(dev, rpmflags);

			return 0;

		}
@@ -1527,14 +1554,17 @@ EXPORT_SYMBOL_GPL(pm_runtime_forbid); 
 */

void pm_runtime_allow(struct device *dev)

{

	int ret;



	spin_lock_irq(&dev->power.lock);

	if (dev->power.runtime_auto)

		goto out;



	dev->power.runtime_auto = true;

	if (atomic_dec_and_test(&dev->power.usage_count))

	ret = rpm_drop_usage_count(dev);

	if (ret == 0)

		rpm_idle(dev, RPM_AUTO | RPM_ASYNC);

	else

	else if (ret > 0)

		trace_rpm_usage_rcuidle(dev, RPM_AUTO | RPM_ASYNC);



 out: