linux-kernel - [tip: core/rcu] rcu: Clear ->rcu_read_unlock

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Message-ID: <157994896305.396.11466393272376454172.tip-bot2@tip-bot2>
Date:   Sat, 25 Jan 2020 10:42:43 -0000
From:   "tip-bot2 for Lai Jiangshan" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/rcu] rcu: Clear ->rcu_read_unlock_special only once

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     3717e1e9f25ec7059e421ab6fc602cab7063c11c
Gitweb:        https://git.kernel.org/tip/3717e1e9f25ec7059e421ab6fc602cab7063c11c
Author:        Lai Jiangshan <laijs@...ux.alibaba.com>
AuthorDate:    Fri, 01 Nov 2019 05:06:21 -07:00
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Fri, 24 Jan 2020 10:27:33 -08:00

rcu: Clear ->rcu_read_unlock_special only once

In rcu_preempt_deferred_qs_irqrestore(), ->rcu_read_unlock_special is
cleared one piece at a time.  Given that the "if" statements in this
function use the copy in "special", this commit removes the clearing
of the individual pieces in favor of clearing ->rcu_read_unlock_special
in one go just after it has been determined to be non-zero.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_plugin.h | 19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 7487c79..c3a3271 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -444,16 +444,9 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 		local_irq_restore(flags);
 		return;
 	}
-	t->rcu_read_unlock_special.b.exp_hint = false;
-	t->rcu_read_unlock_special.b.deferred_qs = false;
-	if (special.b.need_qs) {
+	t->rcu_read_unlock_special.s = 0;
+	if (special.b.need_qs)
 		rcu_qs();
-		t->rcu_read_unlock_special.b.need_qs = false;
-		if (!t->rcu_read_unlock_special.s && !rdp->exp_deferred_qs) {
-			local_irq_restore(flags);
-			return;
-		}
-	}
 
 	/*
 	 * Respond to a request by an expedited grace period for a
@@ -461,17 +454,11 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 	 * tasks are handled when removing the task from the
 	 * blocked-tasks list below.
 	 */
-	if (rdp->exp_deferred_qs) {
+	if (rdp->exp_deferred_qs)
 		rcu_report_exp_rdp(rdp);
-		if (!t->rcu_read_unlock_special.s) {
-			local_irq_restore(flags);
-			return;
-		}
-	}
 
 	/* Clean up if blocked during RCU read-side critical section. */
 	if (special.b.blocked) {
-		t->rcu_read_unlock_special.b.blocked = false;
 
 		/*
 		 * Remove this task from the list it blocked on.  The task