linux-kernel - [PATCH v2 18/27] rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_changed

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Date: Tue, 30 Apr 2024 11:17:22 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Frederic Weisbecker <frederic@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: [PATCH v2 18/27] rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_changed_since()

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, the dynticks prefix can go.

Furthermore, the "in_eqs_since" part confuses me, as IIUC this only checks
for a change in watching/eqs state, not that RCU transitionned *into* a
EQS after the snapshot was taken.

e.g. if
  snap = 0b1000 (EQS)
and the following rcu_watching_snap(CPU) is:
	 0b1100 (watching)
then
  rcu_watching_in_eqs_since(rdp, snap) -> true

but because RCU was already in EQS at the time of the
snap - it hasn't entered EQS "since" the snap was taken.

Update the name to reflect that we're only looking at watching/EQS
transitions, not specifically transitions into EQS.

Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
 .../RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst   | 2 +-
 kernel/rcu/tree.c                                             | 4 ++--
 kernel/rcu/tree_exp.h                                         | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
index e8ef12ca1e9da..0533814a1f69a 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
@@ -150,7 +150,7 @@ This case is handled by calls to the strongly ordered
 is invoked within ``rcu_dynticks_eqs_enter()`` at idle-entry
 time and within ``rcu_dynticks_eqs_exit()`` at idle-exit time.
 The grace-period kthread invokes ``rcu_watching_snap()`` and
-``rcu_dynticks_in_eqs_since()`` (both of which invoke
+``rcu_watching_changed_since()`` (both of which invoke
 an ``atomic_add_return()`` of zero) to detect idle CPUs.
 
 +-----------------------------------------------------------------------+
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d772755ccd564..ffcde8203c04f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -320,7 +320,7 @@ static bool rcu_watching_in_eqs(int snap)
  * structure has spent some time in an extended quiescent state since
  * rcu_watching_snap() returned the specified snapshot.
  */
-static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
+static bool rcu_watching_changed_since(struct rcu_data *rdp, int snap)
 {
 	return snap != rcu_watching_snap(rdp->cpu);
 }
@@ -803,7 +803,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	 * read-side critical section that started before the beginning
 	 * of the current RCU grace period.
 	 */
-	if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
+	if (rcu_watching_changed_since(rdp, rdp->dynticks_snap)) {
 		trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
 		rcu_gpnum_ovf(rnp, rdp);
 		return 1;
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 68dea1427c8bd..4046fae99517e 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -381,7 +381,7 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 		unsigned long mask = rdp->grpmask;
 
 retry_ipi:
-		if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
+		if (rcu_watching_changed_since(rdp, rdp->exp_dynticks_snap)) {
 			mask_ofl_test |= mask;
 			continue;
 		}
-- 
2.43.0