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    SubjectRe: [PATCH v2 0/6] Rework REFCOUNT_FULL using atomic_fetch_* operations
    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

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