On Mon, 16 Apr 2007 15:38:52 -0400 (EDT), Alan Stern <[EMAIL PROTECTED]> wrote:
> On Mon, 16 Apr 2007, Dmitry Torokhov wrote: > > 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. My current preference is 2. (obviously :)). I don't like 3. too much (too complicated code), but I think it would still be better than 1. (And I agree, this will be harder to trigger with Tejun's patches.) > > (Also, doing this might be a good way to expose a lot of hidden > refcounting bugs. They will become very obvious when rmmod hangs.) Good point. - 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/
