Linux

That's the thing. It doesn't break it to the point of unusable unlike other patches I think. So the test didn't catch this since performance is rarely a part of a test suite no?

I'm not a kernel developer, but it does seem weird to remove the legacy function in the same patch as the replacement function is shipped.

That said, isn't it fairly easy to install a modified kernel? Or is that hard on Ubuntu for some reason? I suppose it's to do with official support cycles and patches, so that's only really a viable fix if the distro manages to kernel options, to ensure timelines with security patches and commercial support.