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From: Marco Elver <elver@google.com>
To: elver@google.com
Cc: paulmck@kernel.org, dvyukov@google.com, glider@google.com,
	andreyknvl@google.com, kasan-dev@googlegroups.com,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	mingo@kernel.org, peterz@infradead.org, will@kernel.org,
	clang-built-linux@googlegroups.com, bp@alien8.de
Subject: [PATCH -tip v2 08/11] READ_ONCE, WRITE_ONCE: Remove data_race() and unnecessary checks
Date: Thu, 21 May 2020 13:08:51 +0200	[thread overview]
Message-ID: <20200521110854.114437-9-elver@google.com> (raw)
In-Reply-To: <20200521110854.114437-1-elver@google.com>

The volatile accesses no longer need to be wrapped in data_race(),
because we require compilers that emit instrumentation distinguishing
volatile accesses. Consequently, we also no longer require the explicit
kcsan_check_atomic*(), since the compiler emits instrumentation
distinguishing the volatile accesses. Finally, simplify
__READ_ONCE_SCALAR and remove __WRITE_ONCE_SCALAR.

Signed-off-by: Marco Elver <elver@google.com>
---
v2:
* Remove unnecessary kcsan_check_atomic*() in *_ONCE.
* Simplify __READ_ONCE_SCALAR and remove __WRITE_ONCE_SCALAR. This
  effectively restores Will Deacon's pre-KCSAN version:
  https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/tree/include/linux/compiler.h?h=rwonce/cleanup#n202
---
 include/linux/compiler.h | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 17c98b215572..7444f026eead 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -228,9 +228,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 
 #define __READ_ONCE_SCALAR(x)						\
 ({									\
-	typeof(x) *__xp = &(x);						\
-	__unqual_scalar_typeof(x) __x = data_race(__READ_ONCE(*__xp));	\
-	kcsan_check_atomic_read(__xp, sizeof(*__xp));			\
+	__unqual_scalar_typeof(x) __x = __READ_ONCE(x);			\
 	smp_read_barrier_depends();					\
 	(typeof(x))__x;							\
 })
@@ -246,17 +244,10 @@ do {									\
 	*(volatile typeof(x) *)&(x) = (val);				\
 } while (0)
 
-#define __WRITE_ONCE_SCALAR(x, val)					\
-do {									\
-	typeof(x) *__xp = &(x);						\
-	kcsan_check_atomic_write(__xp, sizeof(*__xp));			\
-	data_race(({ __WRITE_ONCE(*__xp, val); 0; }));			\
-} while (0)
-
 #define WRITE_ONCE(x, val)						\
 do {									\
 	compiletime_assert_rwonce_type(x);				\
-	__WRITE_ONCE_SCALAR(x, val);					\
+	__WRITE_ONCE(x, val);						\
 } while (0)
 
 #ifdef CONFIG_KASAN
-- 
2.26.2.761.g0e0b3e54be-goog


  parent reply	other threads:[~2020-05-21 11:10 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-21 11:08 [PATCH -tip v2 00/11] Fix KCSAN for new ONCE (require Clang 11) Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 01/11] ubsan, kcsan: don't combine sanitizer with kcov on clang Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 02/11] kcsan: Avoid inserting __tsan_func_entry/exit if possible Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 03/11] kcsan: Support distinguishing volatile accesses Marco Elver
2020-05-21 13:18   ` Will Deacon
2020-05-21 13:26     ` Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 04/11] kcsan: Pass option tsan-instrument-read-before-write to Clang Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 05/11] kcsan: Remove 'noinline' from __no_kcsan_or_inline Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 06/11] kcsan: Restrict supported compilers Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 07/11] kcsan: Update Documentation to change " Marco Elver
2020-05-21 13:33   ` Will Deacon
2020-05-21 13:35     ` Marco Elver
2020-05-21 11:08 ` Marco Elver [this message]
2020-05-21 11:08 ` [PATCH -tip v2 09/11] data_race: Avoid nested statement expression Marco Elver
2020-05-21 13:31   ` Will Deacon
2020-05-21 13:39     ` Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 10/11] compiler.h: Move function attributes to compiler_types.h Marco Elver
2020-05-21 11:08 ` [PATCH -tip v2 11/11] compiler_types.h, kasan: Use __SANITIZE_ADDRESS__ instead of CONFIG_KASAN to decide inlining Marco Elver
2020-05-21 13:36 ` [PATCH -tip v2 00/11] Fix KCSAN for new ONCE (require Clang 11) Will Deacon
2020-05-21 13:42   ` Marco Elver
2020-05-21 13:42     ` Will Deacon

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