[PATCH] rcu-tasks: Update comments in call_rcu_tasks_generic()

[PATCH] rcu-tasks: Update comments in call_rcu_tasks_generic()

[Zqiang]

Currently, the comments: "We can't create the thread unless interrupts
are enabled." from 'commit 4929c913bda5 ("rcu: Make call_rcu_tasks()
tolerate first call with irqs disabled")', now the kthread creation
has been move to core_initcall() time from 'commit c63eb17ff06d
("rcu: Create call_rcu_tasks() kthread at boot time")', and use the
irq_work does deferred wakeup. this commit therefore update comments
in call_rcu_tasks_generic().

Signed-off-by: Zqiang <qiang.zhang@linux.dev>
---
 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 a2ca79d1dd6a..089a0d5a5cc9 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,
+	// or a spinlock might be held, the kthread creation has
+	// been move to core_initcall() time.
+	// at the same time, use the irq_work does deferred wakeup
+	// to avoid potential lockdep splat.
 	if (needwake && READ_ONCE(rtp->kthread_ptr))
 		irq_work_queue(&rtpcp->rtp_irq_work);
 }
-- 
2.17.1

Re: [PATCH] rcu-tasks: Update comments in call_rcu_tasks_generic()

[Paul E. McKenney]

On Mon, Jul 13, 2026 at 06:31:26PM +0800, Zqiang wrote:
> Currently, the comments: "We can't create the thread unless interrupts
> are enabled." from 'commit 4929c913bda5 ("rcu: Make call_rcu_tasks()
> tolerate first call with irqs disabled")', now the kthread creation
> has been move to core_initcall() time from 'commit c63eb17ff06d
> ("rcu: Create call_rcu_tasks() kthread at boot time")', and use the
> irq_work does deferred wakeup. this commit therefore update comments
> in call_rcu_tasks_generic().
> 
> Signed-off-by: Zqiang <qiang.zhang@linux.dev>

Queued and pushed both, thank you!  I adjusted the comment and commit log,
so please double-check them in case I messed something up.

							Thanx, Paul

> ---
>  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 a2ca79d1dd6a..089a0d5a5cc9 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,
> +	// or a spinlock might be held, the kthread creation has
> +	// been move to core_initcall() time.
> +	// at the same time, use the irq_work does deferred wakeup
> +	// to avoid potential lockdep splat.
>  	if (needwake && READ_ONCE(rtp->kthread_ptr))
>  		irq_work_queue(&rtpcp->rtp_irq_work);
>  }
> -- 
> 2.17.1
>