Re: [PATCH printk v2 33/38] printk: introduce console_list_lock

Paul E. McKenney
2022-11-07T16:16:46Z

On Mon, Nov 07, 2022 at 11:16:56AM +0106, John Ogness wrote:
> On 2022-10-27, "Paul E. McKenney" <paulmck@kernel.org> wrote:
> > One way to save a line is as follows:
> >
> > WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC) &&
> > debug_lockdep_rcu_enabled() &&
> > srcu_read_lock_held(&console_srcu));
>
> Unfortunately this suggestion does not work because
> debug_lockdep_rcu_enabled() only exists if CONFIG_DEBUG_LOCK_ALLOC is
> enabled. Would you be interested in having an empty implementation?
> Then my check would not need to be concerned about
> CONFIG_DEBUG_LOCK_ALLOC at all. It would become:
>
> WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
> srcu_read_lock_held(&console_srcu));
>
> The patch below could be used to achieve that.

Looks quite sensible to me! There are probably a few other places
where it might be used.

Thanx, Paul

> John
>
> --------8<-------------
> >From 71d9e484d5128cd1e57e5bff5391d91789f444fa Mon Sep 17 00:00:00 2001
> From: John Ogness <john.ogness@linutronix.de>
> Date: Mon, 7 Nov 2022 11:06:40 +0106
> Subject: [PATCH] rcu: implement lockdep_rcu_enabled for
> !CONFIG_DEBUG_LOCK_ALLOC
>
> Provide an implementation for debug_lockdep_rcu_enabled() when
> CONFIG_DEBUG_LOCK_ALLOC is not enabled. This allows code to check
> if rcu lockdep debugging is available without needing an extra
> check if CONFIG_DEBUG_LOCK_ALLOC is enabled.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
> include/linux/rcupdate.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 08605ce7379d..65178c40ab6f 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -340,6 +340,11 @@ static inline int rcu_read_lock_any_held(void)
> return !preemptible();
> }
>
> +static inline int debug_lockdep_rcu_enabled(void)
> +{
> + return 0;
> +}
> +
> #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> #ifdef CONFIG_PROVE_RCU
> --
> 2.30.2