[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>

5 files changed, 24 insertions, 6 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);
 }
 
 
diff --git a/drivers/base/core.c b/drivers/base/core.c
index a293a788abd4..93440824b800 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -212,6 +212,7 @@ void device_initialize(struct device *dev)
         INIT_LIST_HEAD(&dev->driver_list);
         INIT_LIST_HEAD(&dev->bus_list);
         INIT_LIST_HEAD(&dev->dma_pools);
+        init_MUTEX(&dev->sem);
 }
 
 /**
diff --git a/drivers/base/power/resume.c b/drivers/base/power/resume.c
index 26468971ef5a..bdd96b03b885 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;
 }
 
 
diff --git a/drivers/base/power/suspend.c b/drivers/base/power/suspend.c
index 0ec44ef840be..807e13fb205b 100644
--- a/drivers/base/power/suspend.c
+++ b/drivers/base/power/suspend.c
@@ -39,6 +39,7 @@ int suspend_device(struct device * dev, pm_message_t state)
 {
         int error = 0;
 
+        down(&dev->sem);
         if (dev->power.power_state) {
                 dev_dbg(dev, "PM: suspend %d-->%d\n",
                         dev->power.power_state, state);
@@ -58,7 +59,7 @@ int suspend_device(struct device * dev, pm_message_t state)
                 dev_dbg(dev, "suspending\n");
                 error = dev->bus->suspend(dev, state);
         }
-
+        up(&dev->sem);
         return error;
 }
 
diff --git a/include/linux/device.h b/include/linux/device.h
index 68a95358013d..195b327f3e19 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -264,6 +264,10 @@ struct device {
         struct kobject kobj;
         char    bus_id[BUS_ID_SIZE];    /* position on parent bus */
 
+        struct semaphore        sem;    /* semaphore to synchronize calls to
+                                         * its driver.
+                                         */
+
         struct bus_type * bus;          /* type of bus device is on */
         struct device_driver *driver;   /* which driver has allocated this
                                            device */