Commit 44b97dcc authored May 21, 2020 by Marco Elver Committed by Thomas Gleixner Jun 11, 2020

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.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

parent 0bb9ab3a

include/linux/compiler.h

+2 −11

Original line number	Diff line number	Diff line
		@@ -281,9 +281,7 @@ 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; \
		})
		@@ -299,17 +297,10 @@ 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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