linux-kernel - [PATCH rcu 03/17] srcu: Use ->srcu_gp

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Message-Id: <20250116202112.3783327-3-paulmck@kernel.org>
Date: Thu, 16 Jan 2025 12:20:58 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	bpf@...r.kernel.org
Subject: [PATCH rcu 03/17] srcu: Use ->srcu_gp_seq for rcutorture reader batch

This commit stops using ->srcu_idx for rcutorture's reader-batch
consistency checking, using ->srcu_gp_seq instead.  This is a first
step towards a faster srcu_read_{,un}lock_lite() that avoids the array
accesses that use ->srcu_idx.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: <bpf@...r.kernel.org>
---
 kernel/rcu/rcutorture.c | 2 ++
 kernel/rcu/srcutree.c   | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d26fb1d33ed9a..1d2de50fb5d60 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -791,6 +791,7 @@ static struct rcu_torture_ops srcu_ops = {
 	.readunlock	= srcu_torture_read_unlock,
 	.readlock_held	= torture_srcu_read_lock_held,
 	.get_gp_seq	= srcu_torture_completed,
+	.gp_diff	= rcu_seq_diff,
 	.deferred_free	= srcu_torture_deferred_free,
 	.sync		= srcu_torture_synchronize,
 	.exp_sync	= srcu_torture_synchronize_expedited,
@@ -834,6 +835,7 @@ static struct rcu_torture_ops srcud_ops = {
 	.readunlock	= srcu_torture_read_unlock,
 	.readlock_held	= torture_srcu_read_lock_held,
 	.get_gp_seq	= srcu_torture_completed,
+	.gp_diff	= rcu_seq_diff,
 	.deferred_free	= srcu_torture_deferred_free,
 	.sync		= srcu_torture_synchronize,
 	.exp_sync	= srcu_torture_synchronize_expedited,
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index f87a9fb6d6bb8..b5bb73c877de7 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1679,7 +1679,7 @@ EXPORT_SYMBOL_GPL(srcu_barrier);
  */
 unsigned long srcu_batches_completed(struct srcu_struct *ssp)
 {
-	return READ_ONCE(ssp->srcu_idx);
+	return READ_ONCE(ssp->srcu_sup->srcu_gp_seq);
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
-- 
2.40.1