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Date: Mon, 29 May 2017 01:39:04 -0700
From: Christoph Hellwig <>
To: Kees Cook <>
Cc: Andrew Morton <>,
	Elena Reshetova <>,
	Peter Zijlstra <>,
	Greg KH <>,
	"Eric W. Biederman" <>,
	Ingo Molnar <>,
	Alexey Dobriyan <>,
	"Serge E. Hallyn" <>,,
	Davidlohr Bueso <>,
	Manfred Spraul <>,
	Christoph Hellwig <>,
	"" <>,
	James Bottomley <>,
	"" <>, Ingo Molnar <>,
	Arnd Bergmann <>,
	"David S. Miller" <>,
	Rik van Riel <>,
	linux-arch <>,
	"" <>,
	LKML <>
Subject: Re: [PATCH 0/3] ipc subsystem refcounter conversions

On Sat, May 27, 2017 at 12:58:14PM -0700, Kees Cook wrote:
> FAST_REFCOUNT=n: use function-based refcount_t with cmpxvhg and
> full-verification
> FAST_REFCOUNT=y without arch-specific implementation: use atomic_t
> with no verification (i.e. no functional change from now)
> FAST_REFCOUNT=y with arch-specific implementation: use atomic_t with
> overflow protection
> which means FAST_REFCOUNT would need to be default-on so that mm,
> block, net users will remain happy.
> Does that sound reasonable?

I'd rather turn the options around so that the atomic_t or fast
arch implementations are the defaul.  But either way it needs to
be configurable.  Once that is done we can spread refcount_t everywhere
and everyone will be better off, if only for the documentation value
of the type when they use the atomic_t based implementation.

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