linux-kernel - [PATCH] asm-generic: fix compilation failure in cmpxchg

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Date:   Wed, 22 Mar 2017 12:10:22 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     arnd@...db.de, akpm@...ux-foundation.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] asm-generic: fix compilation failure in cmpxchg_double()

Arnd reported that the new code leads to compilation failures
with some versions of gcc. I've filed gcc issue 72873,
but we need a kernel fix as well.

Remove instrumentation from cmpxchg_double() for now.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Reported-by: Arnd Bergmann <arnd@...db.de>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will.deacon@....com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 include/asm-generic/atomic-instrumented.h | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
index 951bcd083925..de6c2a562a6e 100644
--- a/include/asm-generic/atomic-instrumented.h
+++ b/include/asm-generic/atomic-instrumented.h
@@ -229,18 +229,23 @@ INSTR_RET_BOOL2(add_negative);
 	arch_cmpxchg64_local(____ptr, (old), (new));	\
 })
 
+/*
+ * Originally we had the following code here:
+ *	__typeof__(p1) ____p1 = (p1);
+ *	kasan_check_write(____p1, 2 * sizeof(*____p1));
+ *	arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2));
+ * But it leads to compilation failures (see gcc issue 72873).
+ * So for now it's left non-instrumented.
+ * There are few callers of cmpxchg_double(), so it's not critical.
+ */
 #define cmpxchg_double(p1, p2, o1, o2, n1, n2)				\
 ({									\
-	__typeof__(p1) ____p1 = (p1);					\
-	kasan_check_write(____p1, 2 * sizeof(*____p1));			\
-	arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2));	\
+	arch_cmpxchg_double((p1), (p2), (o1), (o2), (n1), (n2));	\
 })
 
 #define cmpxchg_double_local(p1, p2, o1, o2, n1, n2)			\
 ({									\
-	__typeof__(p1) ____p1 = (p1);					\
-	kasan_check_write(____p1, 2 * sizeof(*____p1));			\
-	arch_cmpxchg_double_local(____p1, (p2), (o1), (o2), (n1), (n2));\
+	arch_cmpxchg_double_local((p1), (p2), (o1), (o2), (n1), (n2));	\
 })
 
 #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
-- 
2.12.1.500.gab5fba24ee-goog