linux-kernel - [PATCH 2/2] x86: implement atomic[64]_dec_if

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Date:	Fri, 26 Feb 2010 12:22:41 +0100
From:	Luca Barbieri <luca@...a-barbieri.com>
To:	mingo@...e.hu
Cc:	hpa@...or.com, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org,
	Luca Barbieri <luca@...a-barbieri.com>
Subject: [PATCH 2/2] x86: implement atomic[64]_dec_if_positive

They were missing.

atomic64_dec_if_positive for x86-32 is implemented in my atomic64
improvements for x86-32 patchset.

Signed-off-by: Luca Barbieri <luca@...a-barbieri.com>
---
 arch/x86/include/asm/atomic.h      |   23 +++++++++++++++++++++++
 arch/x86/include/asm/atomic64_64.h |   23 +++++++++++++++++++++++
 lib/atomic64_test.c                |    2 +-
 3 files changed, 47 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
index 8f8217b..706c694 100644
--- a/arch/x86/include/asm/atomic.h
+++ b/arch/x86/include/asm/atomic.h
@@ -246,6 +246,29 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
 
 #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
 
+/*
+ * atomic_dec_if_positive - decrement by 1 if old value positive
+ * @v: pointer of type atomic_t
+ *
+ * The function returns the old value of *v minus 1, even if
+ * the atomic variable, v, was not decremented.
+ */
+static inline int atomic_dec_if_positive(atomic_t *v)
+{
+	int c, old, dec;
+	c = atomic_read(v);
+	for (;;) {
+		dec = c - 1;
+		if (unlikely(dec < 0))
+			break;
+		old = atomic_cmpxchg((v), c, dec);
+		if (likely(old == c))
+			break;
+		c = old;
+	}
+	return dec;
+}
+
 /**
  * atomic_inc_short - increment of a short integer
  * @v: pointer to type int
diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h
index 51c5b40..4d6e2cd 100644
--- a/arch/x86/include/asm/atomic64_64.h
+++ b/arch/x86/include/asm/atomic64_64.h
@@ -221,4 +221,27 @@ static inline int atomic64_add_unless(atomic64_t *v, long a, long u)
 
 #define atomic64_inc_not_zero(v) atomic64_add_unless((v), 1, 0)
 
+/*
+ * atomic64_dec_if_positive - decrement by 1 if old value positive
+ * @v: pointer of type atomic_t
+ *
+ * The function returns the old value of *v minus 1, even if
+ * the atomic variable, v, was not decremented.
+ */
+static inline long atomic64_dec_if_positive(atomic64_t *v)
+{
+	long c, old, dec;
+	c = atomic64_read(v);
+	for (;;) {
+		dec = c - 1;
+		if (unlikely(dec < 0))
+			break;
+		old = atomic64_cmpxchg((v), c, dec);
+		if (likely(old == c))
+			break;
+		c = old;
+	}
+	return dec;
+}
+
 #endif /* _ASM_X86_ATOMIC64_64_H */
diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c
index 0effcac..58efdab 100644
--- a/lib/atomic64_test.c
+++ b/lib/atomic64_test.c
@@ -112,7 +112,7 @@ static __init int test_atomic64(void)
 	r += one;
 	BUG_ON(v.counter != r);
 
-#if defined(CONFIG_X86_32) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
+#if defined(CONFIG_X86) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
 	INIT(onestwos);
 	BUG_ON(atomic64_dec_if_positive(&v) != (onestwos - 1));
 	r -= one;
-- 
1.6.6.1.476.g01ddb

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