On Sat, 17 May 2014 00:32:10 +0200 (CEST) Jiri Kosina <jkos...@suse.cz> wrote:
> That's true, and we come back to what has been said at the very beginning > for both aproaches -- you can't really get away without manual human > inspection of the patches that are being applied. > > The case you have outlined is indeed problematic for the "lazy switching" > aproach, and can be worked around (interim function, which takes both > mutexes in well defined order, for example). > > You can construct a broken locking scenario for stop_machine() aproach as > well -- consider a case when you are exchaing a function which changes the > locking order of two locks/mutexes. How do you deal with the rest of the > code where the locks are being acquired, but not through the functions > you've exchanged? I'm a bit confused by this. If you change locking order and there's other functions that acquire it in reverse order that's not in the patch, that sounds like you just introduced a new bug. > > So again -- there is no disagreement, I believe, about the fact that "live > patches" can't be reliably auto-generated, and human inspection will > always be necessary. Given the intended use-case (serious CVEs mostly, > handled by distro vendors), this is fine. > Right, I absolutely agree that the real use case is to fix off by one errors and buffer overflows. Anything that is more complex really needs a reboot (at a minimum, a kexec reboot). I know our customers would love to see this upgrading entire kernels, but that's rather unrealistic. Why I still favor the stop_machine approach, is because the method of patching is a bit simpler that way. A "lazy" approach will be more complex and more likely to be buggy. The thing I'm arguing here is not the end result being a problem, but the implementation of the patching itself causing bugs. I rather have a "lazy" approach, but like ftrace and its breakpoint method, the stop_machine approach is the simpler way to make sure the patching works before we try to optimize it. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
