On Fri, 30 Jun 2017, Josh Poimboeuf wrote: > On Mon, Jun 19, 2017 at 06:56:37PM +0200, Miroslav Benes wrote: > > > > > > > I often wonder whether it's really a good idea to even allow the > > > > > unloading of patch modules at all. It adds complexity to the livepatch > > > > > code. Is it worth it? I don't have an answer but I'd be interested in > > > > > other people's opinion. > > > > > > > > I could imagine a situation when a livepatch causes, for example, > > > > performance, problems on a server because of the redirection > > > > to the new code. Then it might be handy to disable the patch > > > > and ftrace handlers completely. > > > > > > Fair enough, though it sounds theoretical. It would be good to know > > > we're supporting actual real world use cases. > > > > We distribute cumulative "replace_all" patches at SUSE. replace_all means > > that all previous patches are reverted in the process of application. All > > livepatch modules with zero refcount are removed. This keeps a number of > > loaded modules low and system's state well defined, which is always a good > > thing, because a customer might run into problems and we'd have to debug > > it. > > We used to have something similar in kpatch. And we recently discovered > that this "replace_all" feature would also be nice to have in livepatch. > > We had a patch B which needed to partially revert patch A. We had to > manually do the revert at a function level, which basically means > repatching the function so that it resembles its original state. > > It would be much more straightforward to be able to tell klp to revert > everything in patch A while applying patch B. Then the func stack would > never have more than one entry. And that would be good for performance > as well. Exactly. It is on my TODO list right after the fake signal. I've been occupied by different things recently but I'll definitely return to it soon. Regards, Miroslav -- 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
