linux-kernel - [PATCH 5/6] kvfree_rcu: clear KRC_MONITOR

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Date:   Wed, 14 Apr 2021 14:12:25 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: [PATCH 5/6] kvfree_rcu: clear KRC_MONITOR_TODO bit once a batch is started

Before attempting of starting a new batch the KRC_MONITOR_TODO
bit is cleared and set back when a previous RCU batch is still
in progress.

Clear the KRC_MONITOR_TODO bit only when a new batch has been
successfully queued, if not, it stays active anyway, thus no
reason in setting it back. Please note that checking/setting
this bit is protected by the krcp->lock spinlock.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 kernel/rcu/tree.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index da3605067cc1..012030cbe55e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3427,16 +3427,14 @@ static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
 					  unsigned long flags)
 {
 	// Attempt to start a new batch.
-	clear_bit(KRC_MONITOR_TODO, &krcp->flags);
-
 	if (queue_kfree_rcu_work(krcp)) {
 		// Success! Our job is done here.
+		clear_bit(KRC_MONITOR_TODO, &krcp->flags);
 		raw_spin_unlock_irqrestore(&krcp->lock, flags);
 		return;
 	}
 
 	// Previous RCU batch still in progress, try again later.
-	set_bit(KRC_MONITOR_TODO, &krcp->flags);
 	schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 	raw_spin_unlock_irqrestore(&krcp->lock, flags);
 }
-- 
2.20.1