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

Will Deacon
2019-08-27T16:32:32Z

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@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