1 files changed, 33 insertions, 0 deletions

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index be1972bd2729..59aa43cb146e 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -41,6 +41,39 @@ SYSCALL_DEFINE0(arc_gettls)
         return task_thread_info(current)->thr_ptr;
 }
 
+SYSCALL_DEFINE3(arc_usr_cmpxchg, int *, uaddr, int, expected, int, new)
+{
+        int uval;
+        int ret;
+
+        /*
+         * This is only for old cores lacking LLOCK/SCOND, which by defintion
+         * can't possibly be SMP. Thus doesn't need to be SMP safe.
+         * And this also helps reduce the overhead for serializing in
+         * the UP case
+         */
+        WARN_ON_ONCE(IS_ENABLED(CONFIG_SMP));
+
+        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
+                return -EFAULT;
+
+        preempt_disable();
+
+        ret = __get_user(uval, uaddr);
+        if (ret)
+                goto done;
+
+        if (uval != expected)
+                ret = -EAGAIN;
+        else
+                ret = __put_user(new, uaddr);
+
+done:
+        preempt_enable();
+
+        return ret;
+}
+
 void arch_cpu_idle(void)
 {
         /* sleep, but enable all interrupts before committing */