On Mon, Apr 16, 2007 at 03:47:13PM -0400, Dmitry Torokhov wrote: > On 4/16/07, Alan Stern <[EMAIL PROTECTED]> wrote: > >On Mon, 16 Apr 2007, Dmitry Torokhov wrote: > > > >> On 4/16/07, Cornelia Huck <[EMAIL PROTECTED]> wrote: > >> > Hi, > >> > > >> > based on the discussion in "How should an exit routine wait for > >> > release() callbacks?", I've cooked up some patches that make module > >> > unload wait until the last reference for a kobject has been dropped. > >> > This should plug the "release function in already deleted module" race; > >> > however, if the last kobject_put() from the module containing the > >> > release function is not in the module's exit function, there's still a > >> > small window (not sure if and how to plug this). > >> > >> Unfortunately all this "wait for refcount in module's exit" schemas > >> lead to the following deadlock: > >> > >> rmmod my_module < /path/to/some/file/incrementing/my/refcount > > > >(Note that this problem will be a lot harder to provoke once Tejun's > >changes to sysfs are in place. But it will still be possible, unless we > >make similar changes to all the other filesystems as well.) > > > >There are three possible approaches to this problem: > > > > 1. Ignore it, as we do now. If someone actually tries running your > > example above, an oops will result when the kobject's release > > method is called after my_module has been unloaded from memory. > > > > 2. Do what Cornelia suggested, and allow the example to deadlock. > > > > 3. Change the module code so that rmmod can return _before_ the > > module is actually unloaded from memory (but after the module's > > exit routine has completed). This will lead to more problems. > > For example, what if someone tries to modprobe my_module back > > again before it has finished unloading? > > > >My feeling is that either a deadlock or more complications with modprobe > >would be preferable to an oops. Your opinion may differ. > > > > What about 4: > > When registering an [k]object increment refcount of module that > provides ->release() function. > > That would normally require ->release function to be placed on > subsystem level to allow unloading individual devices.
But that would also mean that a lot of modules that want to be able to be released whenever they want to today, not be allowed to (network drivers, etc.) thanks, greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
