Index: opal/include/opal/sys/arm/atomic.h
===================================================================
--- opal/include/opal/sys/arm/atomic.h	(revision 26359)
+++ opal/include/opal/sys/arm/atomic.h	(working copy)
@@ -18,47 +18,68 @@
  * $HEADER$
  */
 
+/*
+ * ARMv5 and earlier lack robust atomic operations and therefore this file uses
+ * Linux kernel support where needed.  The kernel also provides memory barriers
+ * and this file uses them for ARMv5 and earlier processors, which lack the
+ * memory barrier instruction.  These kernel functions are available on kernel
+ * versions 2.6.15 and greater; using them will result in undefined behavior on
+ * older kernels.
+ * See Documentation/arm/kernel_user_helpers.txt in the kernel tree for details
+ */
+
 #ifndef OMPI_SYS_ARCH_ATOMIC_H
 #define OMPI_SYS_ARCH_ATOMIC_H 1
 
 #if OPAL_WANT_SMP_LOCKS
 
+#if (OPAL_ASM_ARM_VERSION >= 7)
+
+#define OPAL_HAVE_ATOMIC_MEM_BARRIER 1
+/* use the DMB instruction if available... */
+
 #define MB()  __asm__ __volatile__ ("dmb" : : : "memory")
 #define RMB() __asm__ __volatile__ ("dmb" : : : "memory")
 #define WMB() __asm__ __volatile__ ("dmb" : : : "memory")
 
+#elif (OPAL_ASM_ARM_VERSION == 6)
+
+#define OPAL_HAVE_ATOMIC_MEM_BARRIER 1
+/* ...or the v6-specific equivalent... */
+
+#define MB()  __asm__ __volatile__ ("mcr p15, 0, r0, c7, c10, 5" : : : "memory")
+#define RMB() MB()
+#define WMB() MB()
+
 #else
 
-#define MB()
-#define RMB()
-#define WMB()
+#define OPAL_HAVE_ATOMIC_MEM_BARRIER 1
+/* ...otherwise use the Linux kernel-provided barrier */
 
+#define MB() (*((void (*)(void))(0xffff0fa0)))()
+#define RMB() MB()
+#define WMB() MB()
+
 #endif
 
+#else
 
-/**********************************************************************
- *
- * Define constants for ARMv7
- *
- *********************************************************************/
-#define OPAL_HAVE_ATOMIC_MEM_BARRIER 1
+#define MB()
+#define RMB()
+#define WMB()
 
-#define OPAL_HAVE_ATOMIC_CMPSET_32 1
+#endif /* OPAL_WANT_SMP_LOCKS */
 
-#define OPAL_HAVE_ATOMIC_CMPSET_64 1
 
-#define OPAL_HAVE_ATOMIC_MATH_32 1
-#define OPAL_HAVE_ATOMIC_ADD_32 1
-#define OPAL_HAVE_ATOMIC_SUB_32 1
 
-
 /**********************************************************************
  *
  * Memory Barriers
  *
  *********************************************************************/
-#if OMPI_GCC_INLINE_ASSEMBLY
 
+#if (OPAL_HAVE_ATOMIC_MEM_BARRIER == 1)
+
 static inline
 void opal_atomic_mb(void)
 {
@@ -79,13 +100,19 @@
     WMB();
 }
 
+#endif
 
+
 /**********************************************************************
  *
  * Atomic math operations
  *
  *********************************************************************/
 
+#if (OMPI_GCC_INLINE_ASSEMBLY && (OPAL_ASM_ARM_VERSION >= 6))
+
+#define OPAL_HAVE_ATOMIC_CMPSET_32 1
+#define OPAL_HAVE_ATOMIC_MATH_32 1
 static inline int opal_atomic_cmpset_32(volatile int32_t *addr,
                                         int32_t oldval, int32_t newval)
 {
@@ -131,7 +158,9 @@
     return opal_atomic_cmpset_32(addr, oldval, newval);
 }
 
+#if (OPAL_ASM_SUPPORT_64BIT == 1)
 
+#define OPAL_HAVE_ATOMIC_CMPSET_64 1
 static inline int opal_atomic_cmpset_64(volatile int64_t *addr,
                                         int64_t oldval, int64_t newval)
 {
@@ -181,7 +210,10 @@
     return opal_atomic_cmpset_64(addr, oldval, newval);
 }
 
+#endif
 
+
+#define OPAL_HAVE_ATOMIC_ADD_32 1
 static inline int32_t opal_atomic_add_32(volatile int32_t* v, int inc)
 {
    int32_t t;
@@ -202,7 +234,7 @@
    return t;
 }
 
-
+#define OPAL_HAVE_ATOMIC_SUB_32 1
 static inline int32_t opal_atomic_sub_32(volatile int32_t* v, int dec)
 {
    int32_t t;
@@ -222,7 +254,30 @@
    return t;
 }
 
+#else /* OPAL_ASM_ARM_VERSION <=5 or no GCC inline assembly */
 
-#endif /* OMPI_GCC_INLINE_ASSEMBLY */
+#define OPAL_HAVE_ATOMIC_CMPSET_32 1
+#define __kuser_cmpxchg (*((int (*)(int, int, volatile int*))(0xffff0fc0)))
+static inline int opal_atomic_cmpset_32(volatile int32_t *addr,
+                                        int32_t oldval, int32_t newval)
+{
+    return !(__kuser_cmpxchg(oldval, newval, addr));
+}
 
+static inline int opal_atomic_cmpset_acq_32(volatile int32_t *addr,
+                                            int32_t oldval, int32_t newval)
+{
+    /* kernel function includes all necessary memory barriers */
+    return opal_atomic_cmpset_32(addr, oldval, newval);
+}
+
+static inline int opal_atomic_cmpset_rel_32(volatile int32_t *addr,
+                                            int32_t oldval, int32_t newval)
+{
+    /* kernel function includes all necessary memory barriers */
+    return opal_atomic_cmpset_32(addr, oldval, newval);
+}
+
+#endif
+
 #endif /* ! OMPI_SYS_ARCH_ATOMIC_H */
Index: opal/config/opal_config_asm.m4
===================================================================
--- opal/config/opal_config_asm.m4	(revision 26359)
+++ opal/config/opal_config_asm.m4	(working copy)
@@ -915,9 +915,31 @@
         armv7*)
             ompi_cv_asm_arch="ARM"
             OPAL_ASM_SUPPORT_64BIT=1
+            OPAL_ASM_ARM_VERSION=7
+            AC_DEFINE_UNQUOTED([OPAL_ASM_ARM_VERSION], [$OPAL_ASM_ARM_VERSION],
+                               [What ARM assembly version to use])
             OMPI_GCC_INLINE_ASSIGN='"mov %0, #0" : "=&r"(ret)'
             ;;
 
+        armv6*)
+            ompi_cv_asm_arch="ARM"
+            OPAL_ASM_SUPPORT_64BIT=0
+            OPAL_ASM_ARM_VERSION=6
+            AC_DEFINE_UNQUOTED([OPAL_ASM_ARM_VERSION], [$OPAL_ASM_ARM_VERSION],
+                               [What ARM assembly version to use])
+            OMPI_GCC_INLINE_ASSIGN='"mov %0, #0" : "=&r"(ret)'
+            ;;
+
+        armv5*linux*|armv4*linux*)
+            # uses Linux kernel helpers for some atomic operations
+            ompi_cv_asm_arch="ARM"
+            OPAL_ASM_SUPPORT_64BIT=0
+            OPAL_ASM_ARM_VERSION=5
+            AC_DEFINE_UNQUOTED([OPAL_ASM_ARM_VERSION], [$OPAL_ASM_ARM_VERSION],
+                               [What ARM assembly version to use])
+            OMPI_GCC_INLINE_ASSIGN='"mov %0, #0" : "=&r"(ret)'
+            ;;
+
         mips-*|mips64*)
             # Should really find some way to make sure that we are on
             # a MIPS III machine (r4000 and later)