rcu: Use RCU's online-CPU state for expedited IPI retry

This commit improves the accuracy of the interaction between CPU hotplug
operations and RCU's expedited grace periods by using RCU's online-CPU
state to determine when failed IPIs should be retried.

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

1 files changed, 5 insertions, 6 deletions

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 3bc4b3dda801..24343eb87b58 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -385,17 +385,16 @@ retry_ipi:
                                 mask_ofl_ipi &= ~mask;
                                 continue;
                         }
-                        /* Failed, raced with offline. */
+                        /* Failed, raced with CPU hotplug operation. */
                         raw_spin_lock_irqsave_rcu_node(rnp, flags);
-                        if (cpu_online(cpu) &&
+                        if ((rnp->qsmaskinitnext & mask) &&
                             (rnp->expmask & mask)) {
+                                /* Online, so delay for a bit and try again. */
                                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
                                 schedule_timeout_uninterruptible(1);
-                                if (cpu_online(cpu) &&
-                                    (rnp->expmask & mask))
-                                        goto retry_ipi;
-                                raw_spin_lock_irqsave_rcu_node(rnp, flags);
+                                goto retry_ipi;
                         }
+                        /* CPU really is offline, so we can ignore it. */
                         if (!(rnp->expmask & mask))
                                 mask_ofl_ipi &= ~mask;
                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);