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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@google.com>
AuthorDate: Thu, 21 May 2020 16:20:44 +02:00
Committer: Borislav Petkov <bp@suse.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@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.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
\
 
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