linux-kernel - Re: [PATCH printk v2 11/11] lockdep: Add atomic write enforcement for lockdep splats

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Date:   Fri, 29 Sep 2023 10:31:41 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH printk v2 11/11] lockdep: Add atomic write enforcement
 for lockdep splats

On Wed 2023-09-20 01:14:56, John Ogness wrote:
> Invoke the atomic write enforcement functions for lockdep
> splats to ensure that the information gets out to the consoles.
> 
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3967,9 +3968,13 @@ static void
>  print_usage_bug(struct task_struct *curr, struct held_lock *this,
>  		enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
>  {
> +	enum nbcon_prio prev_prio;
> +
>  	if (!debug_locks_off() || debug_locks_silent)
>  		return;
>  
> +	prev_prio = nbcon_atomic_enter(NBCON_PRIO_EMERGENCY);
> +
>  	pr_warn("\n");
>  	pr_warn("================================\n");
>  	pr_warn("WARNING: inconsistent lock state\n");
> @@ -3998,6 +4003,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
>  
>  	pr_warn("\nstack backtrace:\n");
>  	dump_stack();
> +
> +	nbcon_atomic_exit(NBCON_PRIO_EMERGENCY, prev_prio);
>  }

The location of the emergency context looks good. I have just proposed
another way for tracking the emergency context. It would allow to
call nbcon_emergency_enter()/exit() without any parameter,
see https://lore.kernel.org/r/ZRLBxsXPCym2NC5Q@alley

Best Regards,
Petr