linux-kernel - [PATCH v5 16/18] kcsan: Rework data_race() so that it can be used by READ

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Message-Id: <20200511204150.27858-17-will@kernel.org>
Date:   Mon, 11 May 2020 21:41:48 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     elver@...gle.com, tglx@...utronix.de, paulmck@...nel.org,
        mingo@...nel.org, peterz@...radead.org, will@...nel.org
Subject: [PATCH v5 16/18] kcsan: Rework data_race() so that it can be used by READ_ONCE()

Rework the data_race() macro so that it:

  - Accepts expressions which evaluate to a 'const' type
  - Attempts to discard volatile qualifiers from scalar types, avoiding
    pointless stack spills
  - Uses __kcsan_{disable,enable}_current(), allowing its use from code
    that is built independently from the kernel, such as the vDSO

This will allow for its use by {READ,WRITE}_ONCE() in a subsequent patch.
At the same time, fix-up some weird whitespace issues.

Cc: Marco Elver <elver@...gle.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 include/linux/compiler.h | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 0caced170a8a..f2a64195ee8e 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -314,14 +314,15 @@ unsigned long read_word_at_a_time(const void *addr)
  * This macro *does not* affect normal code generation, but is a hint
  * to tooling that data races here are to be ignored.
  */
-#define data_race(expr)                                                        \
-	({                                                                     \
-		typeof(({ expr; })) __val;                                     \
-		kcsan_disable_current();                                       \
-		__val = ({ expr; });                                           \
-		kcsan_enable_current();                                        \
-		__val;                                                         \
-	})
+#define data_race(expr)							\
+({									\
+	__kcsan_disable_current();					\
+	({								\
+		__unqual_scalar_typeof(({ expr; })) __v = ({ expr; });	\
+		__kcsan_enable_current();				\
+		__v;							\
+	});								\
+})
 #else
 
 #endif /* __KERNEL__ */
-- 
2.26.2.645.ge9eca65c58-goog