linux-kernel - [PATCH 04/11] rcu: cleanup rcu_preempt_deferred

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Date:   Thu, 31 Oct 2019 10:07:59 +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 04/11] rcu: cleanup rcu_preempt_deferred_qs()

Don't need to set ->rcu_read_lock_nesting negative, irq-protected
rcu_preempt_deferred_qs_irqrestore() doesn't expect
->rcu_read_lock_nesting to be negative to work, it even
doesn't access to ->rcu_read_lock_nesting any more.

It is true that NMI over rcu_preempt_deferred_qs_irqrestore()
may access to ->rcu_read_lock_nesting, but it is still safe
since rcu_read_unlock_special() can protect itself from NMI.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/rcu/tree_plugin.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 82595db04eec..9fe8138ed3c3 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -555,16 +555,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 static void rcu_preempt_deferred_qs(struct task_struct *t)
 {
 	unsigned long flags;
-	bool couldrecurse = t->rcu_read_lock_nesting >= 0;
 
 	if (!rcu_preempt_need_deferred_qs(t))
 		return;
-	if (couldrecurse)
-		t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
 	local_irq_save(flags);
 	rcu_preempt_deferred_qs_irqrestore(t, flags);
-	if (couldrecurse)
-		t->rcu_read_lock_nesting += RCU_NEST_BIAS;
 }
 
 /*
-- 
2.20.1