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);
Thanks,
--
Ming Lei
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