linux-kernel - [PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if

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Message-ID: <20250911125155.680960-1-qiang.zhang@linux.dev>
Date: Thu, 11 Sep 2025 20:51:55 +0800
From: Zqiang <qiang.zhang@...ux.dev>
To: paulmck@...nel.org,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joelagnelf@...dia.com,
	boqun.feng@...il.com,
	urezki@...il.com
Cc: qiang.zhang@...ux.dev,
	rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

Currently, the srcu_gp_start_if_needed() is always be invoked in
preempt disable's critical section, this commit therefore remove
redundant preempt_disable/enable() in srcu_gp_start_if_needed()
and adds a call to lockdep_assert_preemption_disabled() in order
to enable lockdep to diagnose mistaken invocations of this function
from preempts-enabled code.

Fixes: 65b4a59557f6 ("srcu: Make Tiny SRCU explicitly disable preemption")
Signed-off-by: Zqiang <qiang.zhang@...ux.dev>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/srcutiny.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index b52ec45698e8..3450c3751ef7 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
 {
 	unsigned long cookie;
 
-	preempt_disable();  // Needed for PREEMPT_LAZY
+	lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY
 	cookie = get_state_synchronize_srcu(ssp);
 	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
-		preempt_enable();
 		return;
 	}
 	WRITE_ONCE(ssp->srcu_idx_max, cookie);
@@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
 		else if (list_empty(&ssp->srcu_work.entry))
 			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
 	}
-	preempt_enable();
 }
 
 /*
-- 
2.48.1