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From: Lai Jiangshan <laijs@linux.alibaba.com>
To: linux-kernel@vger.kernel.org
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	rcu@vger.kernel.org
Subject: [PATCH 05/11] rcu: clean all rcu_read_unlock_special after report qs
Date: Thu, 31 Oct 2019 10:08:00 +0000	[thread overview]
Message-ID: <20191031100806.1326-6-laijs@linux.alibaba.com> (raw)
In-Reply-To: <20191031100806.1326-1-laijs@linux.alibaba.com>

rcu_preempt_deferred_qs_irqrestore() is always called when
->rcu_read_lock_nesting <= 0 and there is nothing to prevent it
from reporting qs if needed which means ->rcu_read_unlock_special
is better to be clearred after the function. But in some cases,
it leaves exp_hint (for example, after rcu_note_context_switch()),
which is harmess since it is just a hint, but it may also intruduce
unneeded rcu_read_unlock_special() later.

The new code write to exp_hint without WRITE_ONCE() since the
writing is protected by irq.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9fe8138ed3c3..bb3bcdb5c9b8 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -439,6 +439,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 	 * t->rcu_read_unlock_special cannot change.
 	 */
 	special = t->rcu_read_unlock_special;
+	t->rcu_read_unlock_special.b.exp_hint = false;
 	t->rcu_read_unlock_special.b.deferred_qs = false;
 	if (special.b.need_qs) {
 		rcu_qs();
@@ -626,7 +627,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
 		local_irq_restore(flags);
 		return;
 	}
-	WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
 	rcu_preempt_deferred_qs_irqrestore(t, flags);
 }
 
-- 
2.20.1


  parent reply	other threads:[~2019-10-31 10:08 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-31 10:07 [PATCH 00/11] rcu: introduce percpu rcu_preempt_depth Lai Jiangshan
2019-10-31 10:07 ` [PATCH 01/11] rcu: avoid leaking exp_deferred_qs into next GP Lai Jiangshan
2019-10-31 13:43   ` Paul E. McKenney
2019-10-31 18:19     ` Lai Jiangshan
2019-10-31 19:00       ` Paul E. McKenney
2019-10-31 10:07 ` [PATCH 02/11] rcu: fix bug when rcu_exp_handler() in nested interrupt Lai Jiangshan
2019-10-31 13:47   ` Paul E. McKenney
2019-10-31 14:20     ` Lai Jiangshan
2019-10-31 14:31     ` Paul E. McKenney
2019-10-31 15:14       ` Lai Jiangshan
2019-10-31 18:52         ` Paul E. McKenney
2019-11-01  0:19           ` Boqun Feng
2019-11-01  2:29             ` Lai Jiangshan
2019-10-31 10:07 ` [PATCH 03/11] rcu: clean up rcu_preempt_deferred_qs_irqrestore() Lai Jiangshan
2019-10-31 13:52   ` Paul E. McKenney
2019-10-31 15:25     ` Lai Jiangshan
2019-10-31 18:57       ` Paul E. McKenney
2019-10-31 19:02         ` Paul E. McKenney
2019-10-31 10:07 ` [PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs() Lai Jiangshan
2019-10-31 14:10   ` Paul E. McKenney
2019-10-31 14:35     ` Lai Jiangshan
2019-10-31 15:07       ` Paul E. McKenney
2019-10-31 18:33         ` Lai Jiangshan
2019-10-31 22:45           ` Paul E. McKenney
2019-10-31 10:08 ` Lai Jiangshan [this message]
2019-11-01 11:54   ` [PATCH 05/11] rcu: clean all rcu_read_unlock_special after report qs Paul E. McKenney
2019-10-31 10:08 ` [PATCH 06/11] rcu: clear t->rcu_read_unlock_special in one go Lai Jiangshan
2019-11-01 12:10   ` Paul E. McKenney
2019-11-01 16:58     ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 07/11] rcu: set special.b.deferred_qs before wake_up() Lai Jiangshan
2019-10-31 10:08 ` [PATCH 08/11] rcu: don't use negative ->rcu_read_lock_nesting Lai Jiangshan
2019-11-01 12:33   ` Paul E. McKenney
2019-11-16 13:04     ` Lai Jiangshan
2019-11-17 21:53       ` Paul E. McKenney
2019-11-18  1:54         ` Lai Jiangshan
2019-11-18 14:57           ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 09/11] rcu: wrap usages of rcu_read_lock_nesting Lai Jiangshan
2019-10-31 10:08 ` [PATCH 10/11] rcu: clear the special.b.need_qs in rcu_note_context_switch() Lai Jiangshan
2019-10-31 10:08 ` [PATCH 11/11] x86,rcu: use percpu rcu_preempt_depth Lai Jiangshan
2019-11-01 12:58   ` Paul E. McKenney
2019-11-01 13:13     ` Peter Zijlstra
2019-11-01 14:30       ` Paul E. McKenney
2019-11-01 15:32         ` Lai Jiangshan
2019-11-01 16:21           ` Paul E. McKenney
2019-11-01 15:47       ` Lai Jiangshan

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