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

Paul E. McKenney
2022-06-20T22:55:50Z

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@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.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