[PATCH 10/16] rcu: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY

Frederic Weisbecker
2020-10-23T14:47:30Z

Make sure to handle the pending bypass queue before we switch to the
final de-offload state. We'll have to be careful and later set
SEGCBLIST_SOFTIRQ_ONLY before re-enabling again IRQs, or new bypass
callbacks could be queued in the meantine.

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>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
---
kernel/rcu/tree_plugin.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c44b83b79196..49bd42995ae7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2342,12 +2342,19 @@ 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));
+ rcu_nocb_lock_irqsave(rdp, flags);
/* Make sure nocb timer won't stay around */
- rcu_nocb_lock_irqsave(rdp, flags);
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_flush_bypass(rdp, NULL, jiffies);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+
return ret;
}

--
2.25.1