linux-kernel - [PATCH v2 0/6] Rework REFCOUNT_FULL using atomic_fetch

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Date:   Tue, 27 Aug 2019 17:31:58 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>, Kees Cook <keescook@...omium.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>,
        Jan Glauber <jglauber@...vell.com>
Subject: [PATCH v2 0/6] Rework REFCOUNT_FULL using atomic_fetch_* operations

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% )

Cheers,

Will

Cc: Kees Cook <keescook@...omium.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Elena Reshetova <elena.reshetova@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Hanjun Guo <guohanjun@...wei.com>
Cc: Jan Glauber <jglauber@...vell.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