[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, 11 insertions, 3 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 80ce88de56fa..aa27f76d28cd 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -283,18 +283,22 @@ void device_bind_driver(struct device * dev)
  */
 int driver_probe_device(struct device_driver * drv, struct device * dev)
 {
+        int error = 0;
+
         if (drv->bus->match && !drv->bus->match(dev, drv))
                 return -ENODEV;
 
+        down(&dev->sem);
         dev->driver = drv;
         if (drv->probe) {
-                int error = drv->probe(dev);
+                error = drv->probe(dev);
                 if (error) {
                         dev->driver = NULL;
+                        up(&dev->sem);
                         return error;
                 }
         }
-
+        up(&dev->sem);
         device_bind_driver(dev);
         return 0;
 }
@@ -385,7 +389,10 @@ void driver_attach(struct device_driver * drv)
 
 void device_release_driver(struct device * dev)
 {
-        struct device_driver * drv = dev->driver;
+        struct device_driver * drv;
+
+        down(&dev->sem);
+        drv = dev->driver;
         if (drv) {
                 sysfs_remove_link(&drv->kobj, kobject_name(&dev->kobj));
                 sysfs_remove_link(&dev->kobj, "driver");
@@ -394,6 +401,7 @@ void device_release_driver(struct device * dev)
                         drv->remove(dev);
                 dev->driver = NULL;
         }
+        up(&dev->sem);
 }