Messages in this thread | | | Date | Fri, 25 Apr 2014 09:59:53 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] USB: serial: fix sysfs-attribute removal deadlock |
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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.
> 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...
Alan Stern
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