Messages in this thread | | | From | Rusty Russell <> | Subject | Re: Is module refcounting racy? | Date | Tue, 6 Apr 2010 12:09:10 +0930 |
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On Fri, 2 Apr 2010 02:25:59 am Linus Torvalds wrote: > > On Thu, 1 Apr 2010, Nick Piggin wrote: > > > > I think it can be done racelessly with my patch, which is not really too > > much overhead. I think if this is considered too much, then we should > > either fix code and preferably de-export and remove module_refcount from > > drivers, or remove module removal completely. > > I doubt your patch matters too much, but I like it conceptually and it > seems to be a nice basis for perhaps doing something clever in the long > run. > > [ ie avoiding the stop_machine and instead perhaps doing some optimistic > thing like "see if we seem to be unused right now, then unregister us, > and see - after unregistering - that the usage counts haven't increased, > and re-register if they have. ]
I dislike that we can see spurious failure for some random try_module_get caller.
But perhaps that's inherent in module removal: someone can miss out, and if you care, don't try to remove modules.
And grepping for try_module_get() reveals a suspicious (growing) number of try_module_get(THIS_MODULE) which is almost always wrong. If we're not perfect, maybe we should aim for simple?
> So I'd like to apply it as a "good improvement, even if module unloading > which is the only thing that _should_ care deeply should already be under > stop-machine". > > But I'd like an ack or two first.
Yep.
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Cheers, Rusty.
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