On Fri, Feb 14, 2014 at 12:07:17AM +0000, Russell King - ARM Linux wrote: > On Thu, Feb 13, 2014 at 03:26:06PM -0800, Greg KH wrote: > > On Thu, Feb 13, 2014 at 06:42:49PM +0000, Russell King - ARM Linux wrote: > > > We went through this before, and I stated the paths, and no one disagreed > > > with that. > > > > > > It /is/ racy. > > > > Ok, I just went and looked at the uart driver register path, and I don't > > see the race (note, if there is one, it's there today, regardless of > > this patch). > > The race isn't the uart code, it's the driver model. > > Consider what happens when this happens: > > * Two pl011 devices get registered at the same time by two different > threads. How? What two different busses will see this same device? The amba bus code should prevent that from happening, right? If not, there's bigger problems in that bus code :) That's where this problem should be fixed, if there is one, otherwise this same issue would be there for any type of driver that calles into the uart core, right? > * Both devices have a lock taken on the _device_ itself before matching > against the driver. > > * Both devices get matched to the same driver. > > * Both devices are passed into the driver's probe function. > > * Both check uart_reg.state, both call uart_register_driver() on that > at the same time, which results in two allocations inside > uart_register_driver(), one gets overwritten... > > So, the /only/ thing which stops this happening is that the devices > are generally available before the driver is registered, and driver > registration results in devices being probed serially. Moreover, both > attempt to call tty_register_driver()... one succeeds, the other fails. > > However, what about the userspace bind/unbind methods. Yes, userspace > can ask the driver core to unbind devices from a driver or bind - and > again, there's no per-driver locking here. So, if you can trigger two > concurrent binds from userspace, you hit the same race as above. > > So, if you want to accept these patches, go ahead, introduce races, but > personally I'd recommend plugging these races. The only way to solve this would be to do it in the bus, I don't see anything here that makes it any "racier" than it currently is. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
