On Sun, Sep 16, 2012 at 09:24:43PM +0800, Ming Lei wrote:
> On Sun, Sep 16, 2012 at 4:25 PM, Russell King - ARM Linux
> <li...@arm.linux.org.uk> wrote:
> >
> > It isn't. As I said, it's a race condition due to lack of locking - the
> > driver hasn't been added to the list of drivers at this point:
> >
> > int bus_add_driver(struct device_driver *drv)
> > {
> > ...
> > 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);
> > ...
> > }
> >
> > Notice that the attaching is done _before_ the driver is added to the
> > bus driver list.
>
> Yes, it is a problem since a new device may be added to bus
> and bus_probe_device() may not see the new added driver.
>
> So looks klist_add_tail() should complete before driver_attach()
> inside bus_add_driver().
>
> The attached one line change should fix the problem because the
> below way can guarantee that no probe(dev) may be lost.
>
>
> CPU0 CPU1
> driver_register
> ...
> write(bus->driver_list)
> smp_mb()
> read(bus->device_list)
> ...
> device_add
> /* bus_add_device */
> write(bus->device_list)
> smp_mb()
> /* bus_probe_device*/
> read(bus->driver_list)
>
> And the smp_mb() has been implicit by UNLOCK+LOCK
> of 'klist' according to 'VARIETIES OF MEMORY BARRIER' part
> of Documentation/memory-barriers.txt.
>
> Could you test the below patch to see if it can fix your problem?
>
> 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?
thanks,
greg k-h
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