linux-kernel - Re: [RESEND PATCH v4 03/10] lib/refcount: Remove unused refcount_*

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Message-ID: <201911210910.81231377F@keescook>
Date:   Thu, 21 Nov 2019 09:11:58 -0800
From:   Kees Cook <keescook@...omium.org>
To:     dsterba@...e.cz, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [RESEND PATCH v4 03/10] lib/refcount: Remove unused
 refcount_*_checked() variants

On Thu, Nov 21, 2019 at 03:55:33PM +0100, David Sterba wrote:
> On Thu, Nov 21, 2019 at 11:58:55AM +0000, Will Deacon wrote:
> > The full-fat refcount implementation is exposed via a set of functions
> > suffixed with "_checked()", the idea being that code can choose to use
> > the more expensive, yet more secure implementation on a case-by-case
> > basis.
> > 
> > In reality, this hasn't happened, so with a grand total of zero users,
> > let's remove the checked variants for now by simply dropping the suffix
> > and predicating the out-of-line functions on CONFIG_REFCOUNT_FULL=y.
> 
> I am still interested in the _checked versions and have a WIP patch that
> adds that to btrfs (that was my original plan) but haven't had enough
> time to finalize it. The patch itself is simple, the missing part is to
> understand and document what the saturated counters would do with the
> structures.

The good news is that this series removes the case of refcount_t _not_
being checked, so there's no need for _checked helpers.
CONFIG_REFCOUNT_FULL gets removed because all refcount_t ends up being
checked on all architectures. No extra work needed! :) (See patch 8)

-- 
Kees Cook