To be honest, Linus' rants is making a better point for me. I really feel his pain with overflow_usub, and i feel nothing when reading rewritten version.
That's cultural differences 101
As a simple example: in Canada one might say "please do not feed the animals" in a Zoo. In some other places, for the message to have the same effect it must be as such: "It is expressly forbidden to feed the animals! Those being caught doing so will be expelled from the zoo!"
"And yes, you still could have overflow issues if the whole "hlen + xyz" expression overflows, but quite frankly, the "overflow_usub()" code had that too"
Maybe broken is too strong a word I agree
(I'm referring to the || mtu <= 7 part), which, once you know how usub_overflow works is obvious what it means, but this might not be evident and unnecessarily complicating that snipped
Sometimes 'smart code' is not necessarily better
(I'm open to disagreement, though)
What's more interesting to me is how low-stakes this issue is. Gizmodo wrote an article about it, but really, if you understand kernel C, do you even give a shit about this code? Linus could have said "we're not using GCC builtin overflow intrinics", just like that, one line no punctuation, and the issue would have been settled.
But look at this thread at the number of people who extrapolated from Linus' rant that this code was bad, ruinous, unsafe, "one size fits all" (still scratching my head about that), &c. How many of Linus' defenders actually know what he's ranting about? It looks to me like: not many.
What's funny is, you actually do seem like you know what he's talking about, and even you overshot the mark with "broken". :)
I would argue that it's usually not, especially in large and long lived projects. “Everyone knows that debugging is twice as hard as writing a program”.
And judging by his response, i'd say he did - http://lkml.iu.edu/hypermail/linux/kernel/1510.3/02919.html
He could have just said "overflow_usub? no, not in 2015." and everyone would have agreed with him.
The "rewritten" version is short and to the point. Its clear and it uses neutral language. I read it and immediately understood what the issue is with the proposed code and why the changed code is better.
So for me, the rewritten version was many many times better because I could actually understand it without having to force myself to read something long and horrible.