rcu: Fix for rcuo online-time-creation reorganization bug

Commit 35ce7f29a44a (rcu: Create rcuo kthreads only for onlined CPUs)
contains checks for the case where CPUs are brought online out of
order, re-wiring the rcuo leader-follower relationships as needed.
Unfortunately, this rewiring was broken.  This apparently went undetected
due to the tendency of systems to bring CPUs online in order.  This commit
nevertheless fixes the rewiring.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 6d07fb402e841a657d9e5fe4b528104e0d77fcb0..5053dae4454e50436e41b80e0f765cc3e087a6e7 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2586,9 +2586,13 @@ static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
                        rdp->nocb_leader = rdp_spawn;
                        if (rdp_last && rdp != rdp_spawn)
                                rdp_last->nocb_next_follower = rdp;
-                       rdp_last = rdp;
-                       rdp = rdp->nocb_next_follower;
-                       rdp_last->nocb_next_follower = NULL;
+                       if (rdp == rdp_spawn) {
+                               rdp = rdp->nocb_next_follower;
+                       } else {
+                               rdp_last = rdp;
+                               rdp = rdp->nocb_next_follower;
+                               rdp_last->nocb_next_follower = NULL;
+                       }
                } while (rdp);
                rdp_spawn->nocb_next_follower = rdp_old_leader;
        }