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Subject[PATCH v4 02/10] include/linux/compiler.h: Introduce data_race(expr) macro
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This introduces the data_race(expr) macro, which can be used to annotate
expressions for purposes of (1) documenting, and (2) giving tooling such
as KCSAN information about which data races are deemed "safe".

More context:
http://lkml.kernel.org/r/CAHk-=wg5CkOEF8DTez1Qu0XTEFw_oHhxN98bDnFqbY7HL5AB2g@mail.gmail.com

Signed-off-by: Marco Elver <elver@google.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
---
v4:
* Introduce this patch to KCSAN series.
---
include/linux/compiler.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c42fa83f23fb..7d3e77781578 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -310,6 +310,26 @@ unsigned long read_word_at_a_time(const void *addr)
__u.__val; \
})

+#include <linux/kcsan.h>
+
+/*
+ * data_race: macro to document that accesses in an expression may conflict with
+ * other concurrent accesses resulting in data races, but the resulting
+ * behaviour is deemed safe regardless.
+ *
+ * This macro *does not* affect normal code generation, but is a hint to tooling
+ * that data races here should be ignored.
+ */
+#define data_race(expr) \
+ ({ \
+ typeof(({ expr; })) __val; \
+ kcsan_nestable_atomic_begin(); \
+ __val = ({ expr; }); \
+ kcsan_nestable_atomic_end(); \
+ __val; \
+ })
+#else
+
#endif /* __KERNEL__ */

/*
--
2.24.0.rc1.363.gb1bccd3e3d-goog
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