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Date:   Tue, 27 Aug 2019 10:51:59 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Will Deacon <will@kernel.org>
Cc:     linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Elena Reshetova <elena.reshetova@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Hanjun Guo <guohanjun@huawei.com>,
        Jan Glauber <jglauber@marvell.com>
Subject: Re: [PATCH v2 0/6] Rework REFCOUNT_FULL using atomic_fetch_*
 operations
Message-ID: <201908271051.5B9C9F25@keescook>
References: <20190827163204.29903-1-will@kernel.org>
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On Tue, Aug 27, 2019 at 05:31:58PM +0100, Will Deacon wrote:
> Hi all,
> 
> This is version two of the patches I previously posted here:
> 
>   https://lkml.kernel.org/r/20190802101000.12958-1-will@kernel.org
> 
> Changes since v1 include:
> 
>   * Avoid duplicate WARNs when incrementing from zero
>   * Some crude lktdm perf results to motivate the change:
> 
>     # perf stat -r 3 -B -- echo {ATOMIC,REFCOUNT}_TIMING >/sys/kernel/debug/provoke-crash/DIRECT
> 
>     # arm64
>     ATOMIC_TIMING:					46.50451 +- 0.00134 seconds time elapsed  ( +-  0.00% )
>     REFCOUNT_TIMING (REFCOUNT_FULL, mainline):		77.57522 +- 0.00982 seconds time elapsed  ( +-  0.01% )
>     REFCOUNT_TIMING (REFCOUNT_FULL, this series):	48.7181 +- 0.0256 seconds time elapsed  ( +-  0.05% )
> 
>     # x86
>     ATOMIC_TIMING:					31.6225 +- 0.0776 seconds time elapsed  ( +-  0.25% )
>     REFCOUNT_TIMING (!REFCOUNT_FULL, mainline/x86 asm): 31.6689 +- 0.0901 seconds time elapsed  ( +-  0.28% )
>     REFCOUNT_TIMING (REFCOUNT_FULL, mainline):		53.203 +- 0.138 seconds time elapsed  ( +-  0.26% )
>     REFCOUNT_TIMING (REFCOUNT_FULL, this series):	31.7408 +- 0.0486 seconds time elapsed  ( +-  0.15% )

Nice improvements! :) Please consider the series:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> 
> Cheers,
> 
> Will
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Elena Reshetova <elena.reshetova@intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Hanjun Guo <guohanjun@huawei.com>
> Cc: Jan Glauber <jglauber@marvell.com>
> 
> --->8
> 
> Will Deacon (6):
>   lib/refcount: Define constants for saturation and max refcount values
>   lib/refcount: Ensure integer operands are treated as signed
>   lib/refcount: Remove unused refcount_*_checked() variants
>   lib/refcount: Move bulk of REFCOUNT_FULL implementation into header
>   lib/refcount: Improve performance of generic REFCOUNT_FULL code
>   lib/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions
> 
>  drivers/misc/lkdtm/refcount.c |   8 --
>  include/linux/refcount.h      | 236 +++++++++++++++++++++++++++++++++++++----
>  lib/refcount.c                | 237 +-----------------------------------------
>  3 files changed, 218 insertions(+), 263 deletions(-)
> 
> -- 
> 2.11.0
> 

-- 
Kees Cook