linux-kernel - [PATCH -tip v2 09/11] data_race: Avoid nested statement expression

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Message-Id: <20200521110854.114437-10-elver@google.com>
Date:   Thu, 21 May 2020 13:08:52 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com
Cc:     paulmck@...nel.org, dvyukov@...gle.com, glider@...gle.com,
        andreyknvl@...gle.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...nel.org,
        peterz@...radead.org, will@...nel.org,
        clang-built-linux@...glegroups.com, bp@...en8.de
Subject: [PATCH -tip v2 09/11] data_race: Avoid nested statement expression

It appears that compilers have trouble with nested statements
expressions, as such make the data_race() macro be only a single
statement expression. This will help us avoid potential problems in
future as its usage increases.

Link: https://lkml.kernel.org/r/20200520221712.GA21166@zn.tnic
Signed-off-by: Marco Elver <elver@...gle.com>
---
v2:
* Add patch to series in response to above linked discussion.
---
 include/linux/compiler.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7444f026eead..1f9bd9f35368 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -211,12 +211,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  */
 #define data_race(expr)							\
 ({									\
+	__unqual_scalar_typeof(({ expr; })) __v;			\
 	__kcsan_disable_current();					\
-	({								\
-		__unqual_scalar_typeof(({ expr; })) __v = ({ expr; });	\
-		__kcsan_enable_current();				\
-		__v;							\
-	});								\
+	__v = ({ expr; });						\
+	__kcsan_enable_current();					\
+	__v;								\
 })
 
 /*
-- 
2.26.2.761.g0e0b3e54be-goog