Re: [PATCH] fix bad locking in drivers/base/driver.c
From: Mike Waychison
Date: Tue Jan 25 2005 - 02:35:46 EST
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Greg KH wrote:
> On Mon, Jan 24, 2005 at 07:25:19PM +0100, Jirka Kosina wrote:
>
>>Hi,
>>
>>there has been (for quite some time) a bug in function driver_unregister()
>>- the lock/unlock sequence is protecting nothing and the actual
>>bus_remove_driver() is called outside critical section.
>>
>>Please apply.
>
>
> No, please read the comment in the code about why this is the way it is.
> The code is correct as is.
>
Why don't we clean this up as in the proposed attached patch (against
2.6.10). Compile-tested only.
- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice
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Get rid of semaphore abuse by converting device_driver->unload_sem semaphore to device_driver->unloaded completion.
This should get rid of any confusion as well as save a few bytes in the
process.
Signed-off-by: Mike Waychison <michael.waychison@xxxxxxx>
---
drivers/base/bus.c | 2 +-
drivers/base/driver.c | 13 ++++++-------
include/linux/device.h | 2 +-
3 files changed, 8 insertions(+), 9 deletions(-)
Index: linux-2.6.10/drivers/base/bus.c
===================================================================
--- linux-2.6.10.orig/drivers/base/bus.c 2004-12-24 16:34:26.000000000 -0500
+++ linux-2.6.10/drivers/base/bus.c 2005-01-25 02:14:10.000000000 -0500
@@ -65,7 +65,7 @@ static struct sysfs_ops driver_sysfs_ops
static void driver_release(struct kobject * kobj)
{
struct device_driver * drv = to_driver(kobj);
- up(&drv->unload_sem);
+ complete(&drv->unloaded);
}
static struct kobj_type ktype_driver = {
Index: linux-2.6.10/drivers/base/driver.c
===================================================================
--- linux-2.6.10.orig/drivers/base/driver.c 2004-12-24 16:35:25.000000000 -0500
+++ linux-2.6.10/drivers/base/driver.c 2005-01-25 02:16:31.000000000 -0500
@@ -79,14 +79,14 @@ void put_driver(struct device_driver * d
* since most of the things we have to do deal with the bus
* structures.
*
- * The one interesting aspect is that we initialize @drv->unload_sem
- * to a locked state here. It will be unlocked when the driver
- * reference count reaches 0.
+ * The one interesting aspect is that we setup @drv->unloaded
+ * as a completion that gets complete when the driver reference
+ * count reaches 0.
*/
int driver_register(struct device_driver * drv)
{
INIT_LIST_HEAD(&drv->devices);
- init_MUTEX_LOCKED(&drv->unload_sem);
+ init_completion(&drv->unloaded);
return bus_add_driver(drv);
}
@@ -97,7 +97,7 @@ int driver_register(struct device_driver
*
* Again, we pass off most of the work to the bus-level call.
*
- * Though, once that is done, we attempt to take @drv->unload_sem.
+ * Though, once that is done, we wait until @drv->unloaded is copmleted.
* This will block until the driver refcount reaches 0, and it is
* released. Only modular drivers will call this function, and we
* have to guarantee that it won't complete, letting the driver
@@ -107,8 +107,7 @@ int driver_register(struct device_driver
void driver_unregister(struct device_driver * drv)
{
bus_remove_driver(drv);
- down(&drv->unload_sem);
- up(&drv->unload_sem);
+ wait_for_completion(&drv->unloaded);
}
/**
Index: linux-2.6.10/include/linux/device.h
===================================================================
--- linux-2.6.10.orig/include/linux/device.h 2004-12-24 16:35:28.000000000 -0500
+++ linux-2.6.10/include/linux/device.h 2005-01-25 02:13:13.716384240 -0500
@@ -102,7 +102,7 @@ struct device_driver {
char * name;
struct bus_type * bus;
- struct semaphore unload_sem;
+ struct completion unloaded;
struct kobject kobj;
struct list_head devices;