sparc32: Implement xchg and atomic_xchg using ATOMIC_HASH locks

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@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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 765c1776ec9f..0e69b7e7a439 100644
--- 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);
 
diff --git a/arch/sparc/include/asm/cmpxchg_32.h b/arch/sparc/include/asm/cmpxchg_32.h
index 32c29a133f9d..d38b52dca216 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;
-}
-
+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;
diff --git a/arch/sparc/lib/atomic32.c b/arch/sparc/lib/atomic32.c
index a7c418ac26af..71cd65ab200c 100644
--- a/arch/sparc/lib/atomic32.c
+++ b/arch/sparc/lib/atomic32.c
@@ -45,6 +45,19 @@ ATOMIC_OP(add, +=)
 
 #undef ATOMIC_OP
 
+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;
@@ -137,3 +150,17 @@ 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);