linux-kernel - [PATCH V2 6/7] rcu: clear the special.b.need_qs in rcu_note_context

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Message-Id: <20191102124559.1135-7-laijs@linux.alibaba.com>
Date:   Sat,  2 Nov 2019 12:45:58 +0000
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: [PATCH V2 6/7] rcu: clear the special.b.need_qs in rcu_note_context_switch()

It is better to clear the special.b.need_qs when it is
replaced by special.b.blocked or it is really fulfill its
goal in rcu_preempt_deferred_qs_irqrestore().

It makes rcu_qs() easier to be understood, and also prepares for
the percpu rcu_preempt_depth patch, which reqires rcu_special
bits to be clearred in irq-disable context.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/rcu/tree_plugin.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index eb5906c55c8d..e16c3867d2ff 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -264,8 +264,6 @@ static void rcu_qs(void)
 				       __this_cpu_read(rcu_data.gp_seq),
 				       TPS("cpuqs"));
 		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
-		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
-		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
 	}
 }
 
@@ -297,6 +295,7 @@ void rcu_note_context_switch(bool preempt)
 		/* Possibly blocking in an RCU read-side critical section. */
 		rnp = rdp->mynode;
 		raw_spin_lock_rcu_node(rnp);
+		t->rcu_read_unlock_special.b.need_qs = false;
 		t->rcu_read_unlock_special.b.blocked = true;
 		t->rcu_blocked_node = rnp;
 
-- 
2.20.1