linux-kernel - [tip: locking/kcsan] compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}

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Date:   Fri, 22 May 2020 16:08:46 -0000
From:   "tip-bot2 for Marco Elver" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Marco Elver <elver@...gle.com>, Borislav Petkov <bp@...e.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/kcsan] compiler.h: Remove data_race() and unnecessary
 checks from {READ,WRITE}_ONCE()

The following commit has been merged into the locking/kcsan branch of tip:

Commit-ID:     777f73c4e79106d45b304f6af0d31917864dbdf1
Gitweb:        https://git.kernel.org/tip/777f73c4e79106d45b304f6af0d31917864dbdf1
Author:        Marco Elver <elver@...gle.com>
AuthorDate:    Thu, 21 May 2020 16:20:44 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Fri, 22 May 2020 15:19:53 +02:00

compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}_ONCE()

The volatile accesses no longer need to be wrapped in data_race()
because compilers that emit instrumentation distinguishing volatile
accesses are required for KCSAN.

Consequently, the explicit kcsan_check_atomic*() are no longer required
either since the compiler emits instrumentation distinguishing the
volatile accesses.

Finally, simplify __READ_ONCE_SCALAR() and remove __WRITE_ONCE_SCALAR().

 [ bp: Convert commit message to passive voice. ]

Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Will Deacon <will@...nel.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-9-elver@google.com
---
 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 17c98b2..7444f02 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