linux-kernel - Re: [PATCH next v3 1/2] dump_stack: move cpu lock to printk.c

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Message-ID: <YMnmtXG4WE9/xp8f@google.com>
Date:   Wed, 16 Jun 2021 20:55:33 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH next v3 1/2] dump_stack: move cpu lock to printk.c

On (21/06/16 09:35), John Ogness wrote:
> It isn't about limiting. It is about tracking.

Oh, yes. I missed it.
>
[..]

> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e67dc510fa1b..5376216e4f3d 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3535,7 +3535,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
>  
>  #ifdef CONFIG_SMP
>  static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
> -static bool printk_cpulock_nested;
> +static atomic_t printk_cpulock_nested = ATOMIC_INIT(0);
>  
>  /**
>   * __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant
> @@ -3596,7 +3598,7 @@ int __printk_cpu_trylock(void)
>  
>  	} else if (old == cpu) {
>  		/* This CPU is already the owner. */
> -		printk_cpulock_nested = true;
> +		atomic_inc(&printk_cpulock_nested);
>  		return 1;
>  	}
>  
> @@ -3613,8 +3615,8 @@ EXPORT_SYMBOL(__printk_cpu_trylock);
>   */
>  void __printk_cpu_unlock(void)
>  {
> -	if (printk_cpulock_nested) {
> -		printk_cpulock_nested = false;
> +	if (atomic_read(&printk_cpulock_nested)) {
> +		atomic_dec(&printk_cpulock_nested);
>  		return;
>  	}

Looks good.