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Date: Thu, 10 Nov 2016 22:39:52 +0100
From: Peter Zijlstra <>
To: David Windsor <>
Cc:, Will Deacon <>,
	Greg KH <>,
	Elena Reshetova <>,
	Arnd Bergmann <>, Thomas Gleixner <>,
	Ingo Molnar <>,
	"H. Peter Anvin" <>,
	LKML <>
Subject: Re: Re: [RFC v4 PATCH 00/13] HARDENED_ATOMIC

On Thu, Nov 10, 2016 at 04:23:08PM -0500, David Windsor wrote:
> Discussions have been occurring since KSPP has begun: do we need a

Note that I was not included in any of that. If you hide in a corner on
the intartubes don't be surprised people have no clue what you're on

> specialized type for reference counters?  Oh, wait, we do: kref.
> Wait!  kref is implemented with atomic_t.
> So, what?  We obviously need an atomicity for a reference counter
> type.  So, do we simply implement the HARDENED_ATOMIC protected
> version of atomic_t "inside" of kref and leave atomic_t alone?

But you could provide a small subset of the atomic_t API for that, under
a different type.

That way you don't get utter shite like atomic_cmpxchg_wrap() for

>From what I can see only all the add/sub variants have overflow checks,
but all the operations get _wrap() prefixes, even where it doesn't make
any bloody sense. _wrap() on bitops?, _wrap() on cmpxchg(). You must be
bloody joking right?

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