Re: 2.6.30-rc6: Reported regressions from 2.6.29

[Kay Sievers <kay.sievers@vrfy.org>]

On Sun, 2009-05-17 at 02:15 +0200, Kay Sievers wrote:
> On Sun, May 17, 2009 at 02:01, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> 
> >        [   10.428691] Error: Driver 'rtc_cmos' is already registered, aborting...
> >
> > but the driver doesn't really care whether that succeeded or not, but then
> > the platform_driver_probe fails (because the thing is already in use), so
> > then it ends up unregistering something that never got registered in the
> > first place.
> >
> > I think this is strictly speaking a bug in driver_unregister(), which is
> > too fragile. If you unregister a drivert that wasn't registered, we
> > shouldn't oops.
> >
> > But we could certainly do it at the rtc-cmos.c level too, and just not
> > unregister it if the registration failed. My gut feel is that we should
> > aim for the core driver helpers to be less fragile, though - we'll always
> > have driver bugs.
> 
> In:
>  driver_remove_file()
> we try to access the private part:
>  sysfs_remove_file(&drv->p->kobj, ...
> and that is NULL, for an unregistered driver, I would expect.
> 
> I'm looking into it.

This makes the oops in the driver-core, caused by the rtc driver
unregister, go away. The original issue is also fixed in the rtc driver
itself.

Thanks,
Kay


From: Kay Sievers <kay.sievers@vrfy.org>
Subject: Driver Core: do not oops when driver_unregister() is called for unregistered drivers

Handle the case someone tries to unregister a non-registered driver
more gracefully.

  Error: Driver 'rtc_cmos' is already registered, aborting...
  BUG: unable to handle kernel NULL pointer dereference at 00000018
  [<c01e16ba>] sysfs_remove_file+0x1/0xf

Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---

 driver.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -257,6 +257,8 @@ EXPORT_SYMBOL_GPL(driver_register);
  */
 void driver_unregister(struct device_driver *drv)
 {
+	if (!drv || !drv->p)
+		return;
 	driver_remove_groups(drv, drv->groups);
 	bus_remove_driver(drv);
 }