linux-kernel - [PATCHv2 05/11] atomics: instrument cmpxchg

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Date:   Mon, 25 Jun 2018 11:59:46 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org, will.deacon@....com,
        peterz@...radead.org, boqun.feng@...il.com
Cc:     Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCHv2 05/11] atomics: instrument cmpxchg_double*()

We currently don't instrument cmpxchg_double() and
cmpxchg_double_local() due to compilation issues reported in the past,
which are supposedly related to GCC bug 72873 [1], reported when GCC 7
was not yet released. This bug only applies to x86-64, and not other
architectures.

While the test case for GCC bug 72873 triggers issues with released
versions of GCC, the instrumented kernel code compiles fine for all
configurations I have tried, and it is unclear how the two cases
are/were related.

As we can't reproduce the kernel build failures, let's instrument
cmpxchg_double*() again. We can revisit the issue if build failures
reappear.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will.deacon@....com>
---
 include/asm-generic/atomic-instrumented.h | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
index 53481b6eacdf..0d4b1d3dbc1e 100644
--- a/include/asm-generic/atomic-instrumented.h
+++ b/include/asm-generic/atomic-instrumented.h
@@ -450,23 +450,18 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v)
 	arch_cmpxchg64_local(__ai_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)				\
 ({									\
-	arch_cmpxchg_double((p1), (p2), (o1), (o2), (n1), (n2));	\
+	typeof(p1) __ai_p1 = (p1);					\
+	kasan_check_write(__ai_p1, 2 * sizeof(*__ai_p1));		\
+	arch_cmpxchg_double(__ai_p1, (p2), (o1), (o2), (n1), (n2));	\
 })
 
-#define cmpxchg_double_local(p1, p2, o1, o2, n1, n2)			\
-({									\
-	arch_cmpxchg_double_local((p1), (p2), (o1), (o2), (n1), (n2));	\
+#define cmpxchg_double_local(p1, p2, o1, o2, n1, n2)				\
+({										\
+	typeof(p1) __ai_p1 = (p1);						\
+	kasan_check_write(__ai_p1, 2 * sizeof(*__ai_p1));			\
+	arch_cmpxchg_double_local(__ai_p1, (p2), (o1), (o2), (n1), (n2));	\
 })
 
 #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
-- 
2.11.0