From 5976694882f6ebccd0cf7c81a6fdf5c1e08d9d67 Mon Sep 17 00:00:00 2001 From: Zqiang Date: Mon, 13 Jul 2026 18:31:26 +0800 Subject: [PATCH] rcu-tasks: Update comments in call_rcu_tasks_generic() This commit updates the comment "We can't create the thread unless interrupts are enabled." from 'commit 4929c913bda5 ("rcu: Make call_rcu_tasks() tolerate first call with irqs disabled")' to be more clear and also to cover deferred wakeup and to take into account the fact that kthread creation has been move to core_initcall() time by 'commit c63eb17ff06d ("rcu: Create call_rcu_tasks() kthread at boot time")'. Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 79aa5d51388c..bc49698a3bcc 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -395,7 +395,11 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); } rcu_read_unlock(); - /* We can't create the thread unless interrupts are enabled. */ + // We can't create the kthread with interrupts disabled because a + // scheduler spinlock might be held, so kthread creation is deferred + // until core_initcall() time. Similarly, wakeups are deferred using + // irq_work in order to avoid potential scheduler-lock-deadlock + // lockdep splats. if (needwake && READ_ONCE(rtp->kthread_ptr)) irq_work_queue(&rtpcp->rtp_irq_work); }