linux-kernel - Re: [PATCH] printk: nbcon_atomic_flush_pending() is safe only when there is no boot console

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Message-ID: <ZmsLzumVmE3SaG0z@pathway.suse.cz>
Date: Thu, 13 Jun 2024 17:10:06 +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
Subject: Re: [PATCH] printk: nbcon_atomic_flush_pending() is safe only when
 there is no boot console

On Thu 2024-06-13 14:52:24, Petr Mladek wrote:
> Boot consoles are not serialized with the nbcon consoles via the nbcon
> console context or con->device_lock(). The serialization is possible only
> via the legacy console_lock().
> 
> The decision whether nbcon_atomic_flush_pending() should and can be
> called safely is similar and closely related to the decision
> whether the legacy loop should be used.
> 
> Define printing_via_context_safe symmetrically with printing_via_unlock.
> Allow to call nbcon_atomic_flush_pending() only when it is needed and safe.
> 
> --- a/kernel/printk/internal.h
> +++ b/kernel/printk/internal.h
> @@ -192,6 +193,15 @@ extern bool have_legacy_console;
>   */
>  #define printing_via_unlock (have_legacy_console || have_boot_console)
>  
> +/*
> + * Specifies if printing on nbcon consoles is needed and also safe
> + * when serialized only by the nbcon context. If @have_boot_console
> + * is true, the nbcon consoles must be serialized with the boot
> + * consoles using the legacy console_lock().
> + */
> +#define printing_via_context_safe (have_nbcon_console || !have_boot_console)

Oops, this should be:

#define printing_via_context_safe (have_nbcon_console && !have_boot_console)


Best Regards,
Petr