[BUG] Deferred probing in driver model is racy, resulting in lost probes

On Wed, Sep 26, 2012 at 09:23:21PM +0100, Russell King - ARM Linux wrote:

On Wed, Sep 26, 2012 at 01:08:33PM -0700, Greg Kroah-Hartman wrote:

quoted

On Sun, Sep 16, 2012 at 09:24:43PM +0800, Ming Lei wrote:

quoted

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 181ed26..17d7437 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c

@@ -714,12 +714,12 @@ int bus_add_driver(struct device_driver *drv)
 	if (error)
 		goto out_unregister;

+	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
 	if (drv->bus->p->drivers_autoprobe) {
 		error = driver_attach(drv);
 		if (error)
 			goto out_unregister;
 	}
-	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
 	module_add_driver(drv->owner, drv);

 	error = driver_create_file(drv, &driver_attr_uevent);

Did the above patch ever prove to solve the issue or not?

To be honest, I've not bothered to test the above patch, and now when I
look at it, I notice it's broken - in that on error it will corrupt the
driver list.  Take a look at the error path.

priv is drv->p.  We add priv->knode_bus to the driver list.  If
driver_attach() returns an error, then we go to out_unregister, which
does:

out_unregister:
        kobject_put(&priv->kobj);
        kfree(drv->p);
        drv->p = NULL;

thereby freeing the node we just added to the driver list without first
removing it.

I suspect it will fix the problem, but let's get the patch to be correct
before it gets tested...

Good catch.  Ming, care to redo this?

greg k-h