linux-kernel - Re: [PATCH printk v2 33/38] printk: introduce console_list

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Message-ID: <20221107161639.GJ28461@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 7 Nov 2022 08:16:39 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        boqun.feng@...il.com
Subject: Re: [PATCH printk v2 33/38] printk: introduce console_list_lock

On Mon, Nov 07, 2022 at 11:16:56AM +0106, John Ogness wrote:
> On 2022-10-27, "Paul E. McKenney" <paulmck@...nel.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@...utronix.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@...utronix.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