Merge tag 'arc-4.9-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc

[cascardo/linux.git] / arch / arc / kernel / process.c

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index be1972b..59aa43c 100644 (file)
--- 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 */