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Subject[RFC PATCH 09/12] rcu: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading
Date
Set SEGCBLIST_SOFTIRQ_ONLY once everything is settled. After that, the
callbacks are handled locklessly and locally.

Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
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>
---
kernel/rcu/tree_plugin.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index cee15841c178..ef09897c8f2c 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2312,7 +2312,14 @@ static void __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
* enqueued on bypass.
*/
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);
}

static long rcu_nocb_rdp_deoffload(void *arg)
--
2.28.0
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