linux-kernel - Re: [PATCH] console: Replace #if 1 with a bool to ignore WARN_CONSOLE

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Date:   Wed, 11 Jul 2018 21:38:12 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] console: Replace #if 1 with a bool to ignore
 WARN_CONSOLE_UNLOCKED()

Hi,

On 11-07-18 21:17, Steven Rostedt wrote:
> 
> From: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> There's been discussion on the fb list about the addition of
> WARN_CONSOLE_UNLOCKED() inside the fb code. The complaint is that when
> the fb module is loaded with lockless_register_fb the console lock is
> not taken for debugging reasons. With the addition of
> WARN_CONSOLE_UNLOCK() within the fb code, this causes the console to
> fill up with warnings when trying to debug the fb driver.
> 
> There's also a #if 1 that enables the warning which was added before
> git history, and we look down on constant #if's in the kernel nowadays
> anyway.
> 
> Remove the #if 1 and add a ignore_console_lock_warning boolean that can
> be set by drivers to ignore the warning in order to do debugging.
> 
> Link: http://lkml.kernel.org/r/717e6337-e7a6-7a92-1c1b-8929a25696b5@suse.de
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Based on the fbdev discussion this seems a good idea to me
and codewise this looks good to:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans


> ---
> diff --git a/include/linux/console.h b/include/linux/console.h
> index dfd6b0e97855..9d4a6b985154 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -200,11 +200,9 @@ void vcs_make_sysfs(int index);
>   void vcs_remove_sysfs(int index);
>   
>   /* Some debug stub to catch some of the obvious races in the VT code */
> -#if 1
> -#define WARN_CONSOLE_UNLOCKED()	WARN_ON(!is_console_locked() && !oops_in_progress)
> -#else
> -#define WARN_CONSOLE_UNLOCKED()
> -#endif
> +extern bool ignore_console_lock_warning;
> +#define WARN_CONSOLE_UNLOCKED()						\
> +	WARN_ON(!ignore_console_lock_warning && !is_console_locked() && !oops_in_progress)
>   
>   /* VESA Blanking Levels */
>   #define VESA_NO_BLANKING        0
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 247808333ba4..d9056efc3739 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -66,6 +66,9 @@ int console_printk[4] = {
>   	CONSOLE_LOGLEVEL_DEFAULT,	/* default_console_loglevel */
>   };
>   
> +bool ignore_console_lock_warning __read_mostly;
> +EXPORT_SYMBOL(ignore_console_lock_warning);
> +
>   /*
>    * Low level drivers may need that to know if they can schedule in
>    * their unblank() callback or not. So let's export it.
>