1 files changed, 35 insertions, 0 deletions

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index be1972bd2729..a41a79a4f4fe 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -41,6 +41,41 @@ SYSCALL_DEFINE0(arc_gettls)
         return task_thread_info(current)->thr_ptr;
 }
 
+SYSCALL_DEFINE3(arc_usr_cmpxchg, int *, uaddr, int, expected, int, new)
+{
+        struct pt_regs *regs = current_pt_regs();
+        int uval = -EFAULT;
+
+        /*
+         * 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));
+
+        /* Z indicates to userspace if operation succeded */
+        regs->status32 &= ~STATUS_Z_MASK;
+
+        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
+                return -EFAULT;
+
+        preempt_disable();
+
+        if (__get_user(uval, uaddr))
+                goto done;
+
+        if (uval == expected) {
+                if (!__put_user(new, uaddr))
+                        regs->status32 |= STATUS_Z_MASK;
+        }
+
+done:
+        preempt_enable();
+
+        return uval;
+}
+
 void arch_cpu_idle(void)
 {
         /* sleep, but enable all interrupts before committing */