rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY

This commit flushes the bypass queue and sets state to avoid its being
refilled before switching to the final de-offloaded state.  To avoid
refilling, this commit sets SEGCBLIST_SOFTIRQ_ONLY before re-enabling
IRQs.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c88ad62..35dc9b3 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2339,12 +2339,21 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
        swait_event_exclusive(rdp->nocb_state_wq,
                              !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
                                                        SEGCBLIST_KTHREAD_GP));
-       /* Make sure nocb timer won't stay around */
        rcu_nocb_lock_irqsave(rdp, flags);
+       /* Make sure nocb timer won't stay around */
        WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_OFF);
        rcu_nocb_unlock_irqrestore(rdp, flags);
        del_timer_sync(&rdp->nocb_timer);
 
+       /*
+        * Flush bypass. While IRQs are disabled and once we set
+        * SEGCBLIST_SOFTIRQ_ONLY, no callback is supposed to be
+        * enqueued on bypass.
+        */
+       rcu_nocb_lock_irqsave(rdp, flags);
+       rcu_nocb_flush_bypass(rdp, NULL, jiffies);
+       rcu_nocb_unlock_irqrestore(rdp, flags);
+
        return ret;
 }