Messages in this thread | | | Date | Thu, 28 May 2015 11:57:23 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] usb: ulpi: don't register drivers if bus doesn't exist |
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On Thu, 28 May 2015, Felipe Balbi wrote:
> On Thu, May 28, 2015 at 11:09:38AM +0530, Sudip Mukherjee wrote: > > On Wed, May 27, 2015 at 08:21:16AM -0700, Greg KH wrote: > > > On Wed, May 27, 2015 at 11:16:34AM -0400, Alan Stern wrote: > > > > On Wed, 27 May 2015, Heikki Krogerus wrote: > > > > > > Maybe we need to test for this in the driver core, not allowing drivers > > > for busses that are not registered, that might solve the main problem > > > here. I'll try to look at it tonight. > > may i suggest something like this ? > > buildtest with allmodconfig and allyesconfig on x86_64. > > built and booted on x86. > > > > > > diff --git a/drivers/base/bus.c b/drivers/base/bus.c > > index 5005924..95cefa0 100644 > > --- a/drivers/base/bus.c > > +++ b/drivers/base/bus.c > > @@ -943,6 +943,7 @@ int bus_register(struct bus_type *bus) > > if (retval) > > goto bus_groups_fail; > > > > + bus->registered = true; > > once set, it's never cleared.
It's worse than that...
> > pr_debug("bus: '%s': registered\n", bus->name); > > return 0; > > > > diff --git a/drivers/base/driver.c b/drivers/base/driver.c > > index 4eabfe2..1acae5b 100644 > > --- a/drivers/base/driver.c > > +++ b/drivers/base/driver.c > > @@ -150,6 +150,11 @@ int driver_register(struct device_driver *drv) > > int ret; > > struct device_driver *other; > > > > + if (!drv->bus->registered) { > > + pr_err("Driver %s registration failed. bus not yet registered\n", > > + drv->name); > > + return -ENODEV; > > + } > > BUG_ON(!drv->bus->p); > > > > if ((drv->bus->probe && drv->probe) || > > diff --git a/include/linux/device.h b/include/linux/device.h > > index 00ac57c..8fe4745 100644 > > --- a/include/linux/device.h > > +++ b/include/linux/device.h > > @@ -126,6 +126,7 @@ struct bus_type { > > const struct dev_pm_ops *pm; > > > > const struct iommu_ops *iommu_ops; > > + bool registered; /* DON'T TOUCH THIS */ > > I would rather use an atomic_t
What reason is there to use an atomic_t? The value is never going to be changed by two threads at the same time.
More importantly, clearing the flag races with checking it. If somebody tries to register a driver at the same time as the bus is unregistered, the result is undefined.
Of course, the same problem exists when a device is added to a bus at the same time as the bus is unregistered.
Alan Stern
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