linux-kernel - [tip: locking/kcsan] compiler.h: Avoid nested statement expression in data

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Date:   Fri, 22 May 2020 16:08:46 -0000
From:   "tip-bot2 for Marco Elver" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Borislav Petkov <bp@...e.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Marco Elver <elver@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/kcsan] compiler.h: Avoid nested statement expression in
 data_race()

The following commit has been merged into the locking/kcsan branch of tip:

Commit-ID:     aa7d8a2ee1e9b80e36ce2aa0d817c14ab3e23157
Gitweb:        https://git.kernel.org/tip/aa7d8a2ee1e9b80e36ce2aa0d817c14ab3e23157
Author:        Marco Elver <elver@...gle.com>
AuthorDate:    Thu, 21 May 2020 16:20:45 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Fri, 22 May 2020 15:24:21 +02:00

compiler.h: Avoid nested statement expression in data_race()

It appears that compilers have trouble with nested statement
expressions. Therefore, remove one level of statement expression nesting
from the data_race() macro. This will help avoiding potential problems
in the future as its usage increases.

Reported-by: Borislav Petkov <bp@...e.de>
Reported-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Will Deacon <will@...nel.org>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Link: https://lkml.kernel.org/r/20200520221712.GA21166@zn.tnic
Link: https://lkml.kernel.org/r/20200521142047.169334-10-elver@google.com
---
 include/linux/compiler.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7444f02..379a507 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -211,12 +211,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  */
 #define data_race(expr)							\
 ({									\
-	__kcsan_disable_current();					\
-	({								\
-		__unqual_scalar_typeof(({ expr; })) __v = ({ expr; });	\
-		__kcsan_enable_current();				\
-		__v;							\
+	__unqual_scalar_typeof(({ expr; })) __v = ({			\
+		__kcsan_disable_current();				\
+		expr;							\
 	});								\
+	__kcsan_enable_current();					\
+	__v;								\
 })
 
 /*