[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, 2 insertions, 1 deletions

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;
 }