On Mon, 7 May 2018, I wrote:
> On Sun, 6 May 2018, Greg Kroah-Hartman wrote:
>
> > > > Why not just have an "bus is registered" flag in your driver
> > > > register function that refuses to let drivers register with the
> > > > driver core if it isn't set?
> > >
> > > Perhaps that should happen in the core driver_register() function.
> > > BUG_ON is frowned upon, after all. Would that be acceptable?
> >
> > I don't understand what you mean here, perhaps make a patch to show it?
> >
>
> As an alternative to your suggestion (add flag to avoid the BUG_ON):
>
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -148,7 +148,10 @@ int driver_register(struct device_driver *drv)
> int ret;
> struct device_driver *other;
>
> - BUG_ON(!drv->bus->p);
> + if (!drv->bus->p) {
> + WARN_ONCE(1, "Cannot register driver with invalid bus\n");
> + return -EPROBE_DEFER;
> + }
>
> if ((drv->bus->probe && drv->probe) ||
> (drv->bus->remove && drv->remove) ||
>
That rushed example I gave above seems to be confusing the issue. Sorry
about that. (See sioux-core.c for the code that motivated it.)
This example is the sort of flag removal that I had in mind --
diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index ba912558a510..4ee22fb3db92 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -148,7 +148,8 @@ int driver_register(struct device_driver *drv)
int ret;
struct device_driver *other;
- BUG_ON(!drv->bus->p);
+ if (!drv->bus->p)
+ return -ENODEV;
if ((drv->bus->probe && drv->probe) ||
(drv->bus->remove && drv->remove) ||
diff --git a/drivers/visorbus/visorbus_main.c b/drivers/visorbus/visorbus_main.c
index 0b2434cc4ecd..73ff294fd449 100644
--- a/drivers/visorbus/visorbus_main.c
+++ b/drivers/visorbus/visorbus_main.c
@@ -19,8 +19,6 @@ static const guid_t visor_vbus_channel_guid =
VISOR_VBUS_CHANNEL_GUID;
#define LINESIZE 99
#define POLLJIFFIES_NORMALCHANNEL 10
-/* stores whether bus_registration was successful */
-static bool initialized;
static struct dentry *visorbus_debugfs_dir;
/*
@@ -965,9 +963,6 @@ static int visordriver_probe_device(struct device *xdev)
*/
int visorbus_register_visor_driver(struct visor_driver *drv)
{
- /* can't register on a nonexistent bus */
- if (!initialized)
- return -ENODEV;
if (!drv->probe)
return -EINVAL;
if (!drv->remove)
@@ -1212,7 +1207,6 @@ int visorbus_init(void)
err = bus_register(&visorbus_type);
if (err < 0)
return err;
- initialized = true;
bus_device_info_init(&chipset_driverinfo, "chipset", "visorchipset");
return 0;
}
@@ -1229,6 +1223,5 @@ void visorbus_exit(void)
visorbus_remove_instance(dev);
}
bus_unregister(&visorbus_type);
- initialized = false;
debugfs_remove_recursive(visorbus_debugfs_dir);
}
It's very hard to find examples of this pattern, where a flag is used to
inhibit driver_register() calls. As a method of avoiding the BUG_ON this
pattern is not popular.
Hence, the opportunities for flag removal that I mentioned are similarly
rare. So this kind of change is not something I would propose.
Instead I would prefer either of the two solution I've previously sent,
though any one of the 3 would actually resolve the bug reported by
Michael.
In anycase, I'm happy to work on a new solution if it would be more
acceptable. Would you please explain how changing the link order would
avoid the modprobe crash? I still can't figure it out.
--
