linux-kernel - Re: [PATCH printk v2 07/26] printk: Check printk_deferred_enter()/

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Date: Wed, 21 Feb 2024 10:55:38 +0100
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,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH printk v2 07/26] printk: Check
 printk_deferred_enter()/_exit() usage

On Sun 2024-02-18 20:03:07, John Ogness wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> Add validation that printk_deferred_enter()/_exit() are called in
> non-migration contexts.
> 
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -159,13 +159,16 @@ __printf(1, 2) __cold int _printk_deferred(const char *fmt, ...);
>  
>  extern void __printk_safe_enter(void);
>  extern void __printk_safe_exit(void);

It seems that these two does not longer need to stay in
the global linux/printk.h. The declaration can be
moved to kernel/printk/internal.h (with 'extern' removed).

> +extern void __printk_deferred_enter(void);
> +extern void __printk_deferred_exit(void);
> +
>  /*
>   * The printk_deferred_enter/exit macros are available only as a hack for
>   * some code paths that need to defer all printk console printing. Interrupts
>   * must be disabled for the deferred duration.
>   */
> -#define printk_deferred_enter __printk_safe_enter
> -#define printk_deferred_exit __printk_safe_exit
> +#define printk_deferred_enter() __printk_deferred_enter()
> +#define printk_deferred_exit() __printk_deferred_exit()
>  
>  /*
>   * Please don't use printk_ratelimit(), because it shares ratelimiting state
> diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
> index 6d10927a07d8..8d9408d653de 100644
> --- a/kernel/printk/printk_safe.c
> +++ b/kernel/printk/printk_safe.c
> @@ -26,6 +26,18 @@ void __printk_safe_exit(void)
>  	this_cpu_dec(printk_context);
>  }
>  
> +void __printk_deferred_enter(void)
> +{
> +	cant_migrate();
> +	this_cpu_inc(printk_context);

I would prefer to call __printk_safe_enter() here to make
it clear that they update printk_context the same way
and have the same effect.

Let's make compiler to do the inlining.

> +}
> +
> +void __printk_deferred_exit(void)
> +{
> +	cant_migrate();
> +	this_cpu_dec(printk_context);

ditto

> +}
> +
>  asmlinkage int vprintk(const char *fmt, va_list args)
>  {
>  #ifdef CONFIG_KGDB_KDB

With the two changes:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr