On Fri, 2014-04-25 at 09:59 -0400, Alan Stern wrote: > On Fri, 25 Apr 2014, Li Zhong wrote: > > > > No, this isn't self removal. The driver-attribute (not device-attribute) > > > store operation simply grabs a lock that is also held while the driver > > > is being deregistered at module unload. Taking a reference to the module > > > in this case will prevent deregistration while store is running. > > > > > > But it seems like this can be solved for usb-serial by simply not > > > holding the lock while deregistering. > > > > I didn't look carefully about this lock. > > > > But I'm not sure whether there are such requirements for driver > > attributes: > > > > some lock needs be grabbed in the driver attributes store callbacks, and > > the same lock also needs to be grabbed during driver unregister. > > In this case, the lock does _not_ need to be grabbed during driver > unregister. The driver grabs the lock, but it doesn't need to. OK. > > > If we have such requirements currently or in the future, I think they > > could all be solved by breaking active protection after get the module > > reference. > > No! That would be very bad. > > Unloading modules is quite different from unbinding drivers. After the > driver is unbound, its attribute callback routines can continue to run. > But after a driver module has been unloaded, its attribute callback > routines _cannot_ run because they aren't present in memory any more. > > If we allowed a module to be unloaded while one of its callbacks was > running (because active protection was broken), imagine what would > happen... I don't think the module could be unloaded after we increased the module reference counter. Thanks, Zhong > > Alan Stern > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
