Subject: [PATCH 8/9] sparc32: Implement xchg and atomic_xchg using ATOMIC_HASH locks

From: Andreas Larsson <[email-masked]>
Date: Wed, 5 Nov 2014 15:52:08 +0100

[ Upstream commit 1a17fdc4f4ed06b63fac1937470378a5441a663a ]

Atomicity between xchg and cmpxchg cannot be guaranteed when xchg is
implemented with a swap and cmpxchg is implemented with locks.
Without this, e.g. mcs_spin_lock and mcs_spin_unlock are broken.

Signed-off-by: Andreas Larsson <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 arch/sparc/include/asm/atomic_32.h  |  2 +-
 arch/sparc/include/asm/cmpxchg_32.h | 12 ++----------
 arch/sparc/lib/atomic32.c           | 27 +++++++++++++++++++++++++++
 3 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/arch/sparc/include/asm/atomic_32.h b/arch/sparc/include/asm/atomic_32.h
index 905832a..a0ed182 100644
--- a/arch/sparc/include/asm/atomic_32.h
+++ b/arch/sparc/include/asm/atomic_32.h
@@ -21,7 +21,7 @@
 
 extern int __atomic_add_return(int, atomic_t *);
 extern int atomic_cmpxchg(atomic_t *, int, int);
-#define atomic_xchg(v, new) (xchg(&((v)->counter), new))
+extern int atomic_xchg(atomic_t *, int);
 extern int __atomic_add_unless(atomic_t *, int, int);
 extern void atomic_set(atomic_t *, int);
 
diff --git a/arch/sparc/include/asm/cmpxchg_32.h b/arch/sparc/include/asm/cmpxchg_32.h
index 1fae1a0..ae0f9a7 100644
--- a/arch/sparc/include/asm/cmpxchg_32.h
+++ b/arch/sparc/include/asm/cmpxchg_32.h
@@ -11,22 +11,14 @@
 #ifndef __ARCH_SPARC_CMPXCHG__
 #define __ARCH_SPARC_CMPXCHG__
 
-static inline unsigned long xchg_u32(__volatile__ unsigned long *m, unsigned long val)
-{
-	__asm__ __volatile__("swap [%2], %0"
-			     : "=&r" (val)
-			     : "0" (val), "r" (m)
-			     : "memory");
-	return val;
-}
-
+extern unsigned long __xchg_u32(volatile u32 *m, u32 new);
 extern void __xchg_called_with_bad_pointer(void);
 
 static inline unsigned long __xchg(unsigned long x, __volatile__ void * ptr, int size)
 {
 	switch (size) {
 	case 4:
-		return xchg_u32(ptr, x);
+		return __xchg_u32(ptr, x);
 	}
 	__xchg_called_with_bad_pointer();
 	return x;
diff --git a/arch/sparc/lib/atomic32.c b/arch/sparc/lib/atomic32.c
index 1d32b54..8f2f94d 100644
--- a/arch/sparc/lib/atomic32.c
+++ b/arch/sparc/lib/atomic32.c
@@ -40,6 +40,19 @@ int __atomic_add_return(int i, atomic_t *v)
 }
 EXPORT_SYMBOL(__atomic_add_return);
 
+int atomic_xchg(atomic_t *v, int new)
+{
+	int ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(ATOMIC_HASH(v), flags);
+	ret = v->counter;
+	v->counter = new;
+	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);
+	return ret;
+}
+EXPORT_SYMBOL(atomic_xchg);
+
 int atomic_cmpxchg(atomic_t *v, int old, int new)
 {
 	int ret;
@@ -132,3 +145,17 @@ unsigned long __cmpxchg_u32(volatile u32 *ptr, u32 old, u32 new)
 	return (unsigned long)prev;
 }
 EXPORT_SYMBOL(__cmpxchg_u32);
+
+unsigned long __xchg_u32(volatile u32 *ptr, u32 new)
+{
+	unsigned long flags;
+	u32 prev;
+
+	spin_lock_irqsave(ATOMIC_HASH(ptr), flags);
+	prev = *ptr;
+	*ptr = new;
+	spin_unlock_irqrestore(ATOMIC_HASH(ptr), flags);
+
+	return (unsigned long)prev;
+}
+EXPORT_SYMBOL(__xchg_u32);
-- 
1.7.11.7