1 files changed, 22 insertions, 1 deletions

diff --git a/include/asm-x86_64/futex.h b/include/asm-x86_64/futex.h
index 4f4cb3410d06..7d9eb1a84546 100644
--- a/include/asm-x86_64/futex.h
+++ b/include/asm-x86_64/futex.h
@@ -97,7 +97,28 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
 static inline int
 futex_atomic_cmpxchg_inuser(int __user *uaddr, int oldval, int newval)
 {
-        return -ENOSYS;
+        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
+                return -EFAULT;
+
+        __asm__ __volatile__(
+                "1:     " LOCK_PREFIX "cmpxchgl %3, %1          \n"
+
+                "2:     .section .fixup, \"ax\"                 \n"
+                "3:     mov     %2, %0                          \n"
+                "       jmp     2b                              \n"
+                "       .previous                               \n"
+
+                "       .section __ex_table, \"a\"              \n"
+                "       .align  8                               \n"
+                "       .quad   1b,3b                           \n"
+                "       .previous                               \n"
+
+                : "=a" (oldval), "=m" (*uaddr)
+                : "i" (-EFAULT), "r" (newval), "0" (oldval)
+                : "memory"
+        );
+
+        return oldval;
 }
 
 #endif