[PATCH] Add a semaphore to struct device to synchronize calls to its driver.

This adds a per-device semaphore that is taken before every call from the core to a
driver method. This prevents e.g. simultaneous calls to the ->suspend() or ->resume()
and ->probe() or ->release(), potentially saving a whole lot of headaches.

It also moves us a step closer to removing the bus rwsem, since it protects the fields
in struct device that are modified by the core.

Signed-off-by: Patrick Mochel <mochel@digitalimplant.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/base/power/resume.c b/drivers/base/power/resume.c
index 2646897..bdd96b0 100644
--- a/drivers/base/power/resume.c
+++ b/drivers/base/power/resume.c
@@ -22,6 +22,9 @@ extern int sysdev_resume(void);
 
 int resume_device(struct device * dev)
 {
+	int error = 0;
+
+	down(&dev->sem);
 	if (dev->power.pm_parent
 			&& dev->power.pm_parent->power.power_state) {
 		dev_err(dev, "PM: resume from %d, parent %s still %d\n",
@@ -31,9 +34,10 @@ int resume_device(struct device * dev)
 	}
 	if (dev->bus && dev->bus->resume) {
 		dev_dbg(dev,"resuming\n");
-		return dev->bus->resume(dev);
+		error = dev->bus->resume(dev);
 	}
-	return 0;
+	up(&dev->sem);
+	return error;
 }