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

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Message-ID: <87a6539irz.fsf@jogness.linutronix.de>
Date:   Mon, 07 Nov 2022 11:16:56 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     paulmck@...nel.org, Petr Mladek <pmladek@...e.com>
Cc:     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 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.

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