rcu/nocb: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading

This commit sets SEGCBLIST_SOFTIRQ_ONLY once toggling is otherwise fully
complete, allowing further RCU callback manipulation to be carried out
locklessly and locally.

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 35dc9b31e9a4905369309b0b59cfe3062a466dd8..8641b72f6d0d5919c4b55cf75c5ae1b2f72efda8 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2352,7 +2352,14 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
         */
        rcu_nocb_lock_irqsave(rdp, flags);
        rcu_nocb_flush_bypass(rdp, NULL, jiffies);
-       rcu_nocb_unlock_irqrestore(rdp, flags);
+       rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY);
+       /*
+        * With SEGCBLIST_SOFTIRQ_ONLY, we can't use
+        * rcu_nocb_unlock_irqrestore() anymore. Theoretically we
+        * could set SEGCBLIST_SOFTIRQ_ONLY with cb unlocked and IRQs
+        * disabled now, but let's be paranoid.
+        */
+       raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 
        return ret;
 }