linux-kernel - [tip: core/rcu] rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs

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Date:   Fri, 09 Oct 2020 06:35:40 -0000
From:   "tip-bot2 for Neeraj Upadhyay" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Neeraj Upadhyay <neeraju@...eaurora.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/rcu] rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs_rnp()

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

Commit-ID:     9b1ce0acb5e65e9ea1e6b322562d072f9f7d1f6e
Gitweb:        https://git.kernel.org/tip/9b1ce0acb5e65e9ea1e6b322562d072f9f7d1f6e
Author:        Neeraj Upadhyay <neeraju@...eaurora.org>
AuthorDate:    Mon, 22 Jun 2020 23:37:03 +05:30
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Mon, 24 Aug 2020 18:36:06 -07:00

rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs_rnp()

Originally, the call to rcu_preempt_blocked_readers_cgp() from
force_qs_rnp() had to be conditioned on CONFIG_PREEMPT_RCU=y, as in
commit a77da14ce9af ("rcu: Yet another fix for preemption and CPU
hotplug").  However, there is now a CONFIG_PREEMPT_RCU=n definition of
rcu_preempt_blocked_readers_cgp() that unconditionally returns zero, so
invoking it is now safe.  In addition, the CONFIG_PREEMPT_RCU=n definition
of rcu_initiate_boost() simply releases the rcu_node structure's ->lock,
which is what happens when the "if" condition evaluates to false.

This commit therefore drops the IS_ENABLED(CONFIG_PREEMPT_RCU) check,
so that rcu_initiate_boost() is called only in CONFIG_PREEMPT_RCU=y
kernels when there are readers blocking the current grace period.
This does not change the behavior, but reduces code-reader confusion by
eliminating non-CONFIG_PREEMPT_RCU=y calls to rcu_initiate_boost().

Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4770d77..acc926f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2533,8 +2533,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		rcu_state.cbovldnext |= !!rnp->cbovldmask;
 		if (rnp->qsmask == 0) {
-			if (!IS_ENABLED(CONFIG_PREEMPT_RCU) ||
-			    rcu_preempt_blocked_readers_cgp(rnp)) {
+			if (rcu_preempt_blocked_readers_cgp(rnp)) {
 				/*
 				 * No point in scanning bits because they
 				 * are all zero.  But we might need to