[PATCH 3.17 025/141] sparc32: Implement xchg and atomic_xchg using ATOMIC_HASH locks

From: Greg Kroah-Hartman
Date: Wed Nov 19 2014 - 17:37:43 EST


3.17-stable review patch. If anyone has any objections, please let me know.

------------------

From: Andreas Larsson <andreas@xxxxxxxxxxx>

[ 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 <andreas@xxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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(-)

--- a/arch/sparc/include/asm/atomic_32.h
+++ b/arch/sparc/include/asm/atomic_32.h
@@ -22,7 +22,7 @@

int __atomic_add_return(int, atomic_t *);
int atomic_cmpxchg(atomic_t *, int, int);
-#define atomic_xchg(v, new) (xchg(&((v)->counter), new))
+int atomic_xchg(atomic_t *, int);
int __atomic_add_unless(atomic_t *, int, int);
void atomic_set(atomic_t *, int);

--- 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;
-}
-
+unsigned long __xchg_u32(volatile u32 *m, u32 new);
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;
--- a/arch/sparc/lib/atomic32.c
+++ b/arch/sparc/lib/atomic32.c
@@ -40,6 +40,19 @@ int __atomic_add_return(int i, atomic_t
}
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
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);


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