linux-kernel - [PATCH rcu 29/32] rcu-tasks: Disable and enable CPU hotplug in same function

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Message-Id: <20220620225411.3842519-29-paulmck@kernel.org>
Date:   Mon, 20 Jun 2022 15:54:08 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        KP Singh <kpsingh@...nel.org>
Subject: [PATCH rcu 29/32] rcu-tasks: Disable and enable CPU hotplug in same function

The rcu_tasks_trace_pregp_step() function invokes cpus_read_lock() to
disable CPU hotplug, and a later call to the rcu_tasks_trace_postscan()
function invokes cpus_read_unlock() to re-enable it.  This was absolutely
necessary in the past in order to protect the intervening scan of the full
tasks list, but there is no longer such a scan.  This commit therefore
improves readability by moving the cpus_read_unlock() call to the end
of the rcu_tasks_trace_pregp_step() function.  This commit is a pure
code-motion commit without any (intended) change in functionality.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <kafai@...com>
Cc: KP Singh <kpsingh@...nel.org>
---
 kernel/rcu/tasks.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index c2aae2643a0b2..bf9cc5bc4ae52 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1525,6 +1525,9 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
 		}
 		raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
 	}
+
+	// Re-enable CPU hotplug now that the holdout list is populated.
+	cpus_read_unlock();
 }
 
 /*
@@ -1532,9 +1535,6 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
  */
 static void rcu_tasks_trace_postscan(struct list_head *hop)
 {
-	// Re-enable CPU hotplug now that the tasklist scan has completed.
-	cpus_read_unlock();
-
 	// Wait for late-stage exiting tasks to finish exiting.
 	// These might have passed the call to exit_tasks_rcu_finish().
 	synchronize_rcu();
-- 
2.31.1.189.g2e36527f23