On Mon, 4 May 2015, Josh Poimboeuf wrote: > > - the "immediate" one, where the code redirection flip is switched > > unconditionally and immediately (i.e. exactly what we currently have in > > Linus' tree); semantically applicable to many patches, but not all of > > them > > > > - something that fills the "but not all of them" gap above. > > What's the benefit of having the "immediate" model in addition to > the more comprehensive model? Fair enoungh, I agree that in case of the hybrid aproach you're proposing the immediate model is not necessary. > > - the kGraft method is not (yet) able to patch kernel threads, and allows > > for multiple instances of the patched functions to be running in > > parallel (i.e. patch author needs to be aware of this constaint, and > > write the code accordingly) > > Not being able to patch kthreads sounds like a huge drawback, if not a > deal breaker. It depends on bringing some sanity to freezing / parking / signal handling for kthreads, which is an independent work in progress in parallel. > How does the patching state ever reach completion? kthread context always calls the old code and it doesn't block the finalization; that's basically a documented feature for now. That surely is a limitation and something the patch author has to be aware of, but I wouldn't really consider it a show stopper for now, for the reason pointed out above; it'll eventually be made to work, it's not a substantial issue. > I would say it's orders of magnitude more disruptive and much riskier > compared to walking the stacks (again, assuming we can make stack > walking "safe"). Agreed ... under the condition that it can be made really 100% reliable *and* we'd be reasonably sure that we will be able to realistically achieve the same goal on other architectures as well. Have you even started exploring that space, please? Thanks, -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
