Re: [PATCH] workqueue: Drop redundant rcu_read_lock() from dump functions

[Lai Jiangshan]

Hello, Chan

On Sun, Sep 20, 2026 at 10:46 AM Kunwu Chan <kunwu.chan@xxxxxxxxx> wrote:
>
> show_all_workqueues() and show_cpu_pools_busy_workers() are called
> from contexts that already provide RCU read-side protection.
>
> show_all_workqueues() is called from wq_watchdog_timer_fn(), which
> runs in softirq context, and from sysrq_handle_showstate() through
> __handle_sysrq(), which holds rcu_read_lock().
>
> show_cpu_pools_busy_workers() is called from wq_watchdog_timer_fn()
> as well.
>
> Drop the redundant RCU read-side locking from both functions.
>

I don't think relying on other subsystems to already hold RCU is a good idea,
except for contexts like IRQ or scheduler code, but not softirq.

`rcu_read_lock()` has almost no performance cost and makes the required
context clear.

Thanks,
Lai