From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Will Deacon <will@kernel.org>, Kees Cook <keescook@chromium.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: [PATCH 0/6] Rework REFCOUNT_FULL using atomic_fetch_* operations
Date: Fri, 2 Aug 2019 11:09:54 +0100 [thread overview]
Message-ID: <20190802101000.12958-1-will@kernel.org> (raw)
Hi all,
This patch series reworks the generic REFCOUNT_FULL implementation using
atomic_fetch_* operations so that the performance impact of the cmpxchg()
loops is mitigated for common refcount operations. The algorithm was
heavily inspired by Ard's assembly implementation for arm64:
http://lkml.kernel.org/r/20190619105431.2630-1-ard.biesheuvel@linaro.org
but I figured we could achieve something similar using atomics in generic
code.
Although the revised implementation passes all of the lkdtm REFCOUNT
tests, there is a race condition introduced by the deferred saturation
whereby if INT_MIN + 2 tasks take a reference on a refcount at
REFCOUNT_MAX and are each preempted between detecting overflow and
writing the saturated value without being rescheduled, then another task
may end up erroneously freeing the object when it drops the refcount and
sees zero. It doesn't feel like a particularly realistic case to me, but
I thought I should mention it in case somebody else knows better.
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 | 238 +-----------------------------------------
3 files changed, 219 insertions(+), 263 deletions(-)
--
2.11.0
next reply other threads:[~2019-08-02 10:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 10:09 Will Deacon [this message]
2019-08-02 10:09 ` [PATCH 1/6] lib/refcount: Define constants for saturation and max refcount values Will Deacon
2019-08-02 10:09 ` [PATCH 2/6] lib/refcount: Ensure integer operands are treated as signed Will Deacon
2019-08-02 10:09 ` [PATCH 3/6] lib/refcount: Remove unused refcount_*_checked() variants Will Deacon
2019-08-02 10:09 ` [PATCH 4/6] lib/refcount: Move bulk of REFCOUNT_FULL implementation into header Will Deacon
2019-08-02 18:52 ` Peter Zijlstra
2019-08-03 2:23 ` Kees Cook
2019-08-09 16:04 ` Will Deacon
2019-08-12 18:08 ` Kees Cook
2019-08-02 10:09 ` [PATCH 5/6] lib/refcount: Improve performance of generic REFCOUNT_FULL code Will Deacon
2019-08-02 18:55 ` Peter Zijlstra
2019-08-09 15:38 ` Will Deacon
2019-08-02 10:10 ` [PATCH 6/6] lib/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions Will Deacon
2019-08-02 18:49 ` [PATCH 0/6] Rework REFCOUNT_FULL using atomic_fetch_* operations Peter Zijlstra
2019-08-09 15:34 ` Will Deacon
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