rcuscale: Provide clear error when async specified without primitives

Currently, if the rcuscale module's async module parameter is specified
for RCU implementations that do not have async primitives such as RCU
Tasks Rude (which now lacks a call_rcu_tasks_rude() function), there
will be a series of splats due to calls to a NULL pointer.  This commit
therefore warns of this situation, but switches to non-async testing.

Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index c507750e94d811f099f599aaa589bc84125ba945..79e1c32d5c0fab744910dc1c0dc00949a34bfc44 100644 (file)
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -525,7 +525,7 @@ rcu_scale_writer(void *arg)
                        schedule_timeout_idle(torture_random(&tr) % writer_holdoff_jiffies + 1);
                wdp = &wdpp[i];
                *wdp = ktime_get_mono_fast_ns();
-               if (gp_async) {
+               if (gp_async && !WARN_ON_ONCE(!cur_ops->async)) {
 retry:
                        if (!rhp)
                                rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
@@ -597,7 +597,7 @@ retry:
                        i++;
                rcu_scale_wait_shutdown();
        } while (!torture_must_stop());
-       if (gp_async) {
+       if (gp_async && cur_ops->async) {
                cur_ops->gp_barrier();
        }
        writer_n_durations[me] = i_max + 1;