Re: [PATCH v5 1/5] printk: nbcon: Export console_is_usable

[John Ogness <john.ogness@linutronix.de>]

On 2025-09-30, Marcos Paulo de Souza <mpdesouza@suse.com> wrote:
> The helper will be used on KDB code in the next commits.
>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---
>  include/linux/console.h  | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  kernel/printk/internal.h | 44 --------------------------------------------
>  2 files changed, 44 insertions(+), 44 deletions(-)
>
> diff --git a/include/linux/console.h b/include/linux/console.h
> index 8f10d0a85bb4536e4b0dda4e8ccbdf87978bbb4a..67af483574727c00eea1d5a1eacc994755c92607 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -605,6 +605,48 @@ extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
>  extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
>  extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
>  extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt);
> +
> +/*
> + * Check if the given console is currently capable and allowed to print
> + * records. Note that this function does not consider the current context,
> + * which can also play a role in deciding if @con can be used to print
> + * records.
> + */
> +static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
> +{
> +	if (!(flags & CON_ENABLED))
> +		return false;
> +
> +	if ((flags & CON_SUSPENDED))
> +		return false;
> +
> +	if (flags & CON_NBCON) {
> +		/* The write_atomic() callback is optional. */
> +		if (use_atomic && !con->write_atomic)
> +			return false;
> +
> +		/*
> +		 * For the !use_atomic case, @printk_kthreads_running is not
> +		 * checked because the write_thread() callback is also used
> +		 * via the legacy loop when the printer threads are not
> +		 * available.
> +		 */
> +	} else {
> +		if (!con->write)
> +			return false;
> +	}
> +
> +	/*
> +	 * Console drivers may assume that per-cpu resources have been
> +	 * allocated. So unless they're explicitly marked as being able to
> +	 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
> +	 */
> +	if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
> +		return false;
> +
> +	return true;
> +}
> +
>  #else
>  static inline void nbcon_cpu_emergency_enter(void) { }
>  static inline void nbcon_cpu_emergency_exit(void) { }
> @@ -612,6 +654,8 @@ static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return
>  static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
>  static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
>  static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }
> +static inline bool console_is_usable(struct console *con, short flags,
> +				     bool use_atomic) { return false; }
>  #endif
>  
>  extern int console_set_on_cmdline;
> diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
> index f72bbfa266d6c9bbc533661c40386aa5f0df6c8f..7238da161ff9814fe8a22e4836624e50ee5b71d3 100644
> --- a/kernel/printk/internal.h
> +++ b/kernel/printk/internal.h
> @@ -112,47 +112,6 @@ bool nbcon_kthread_create(struct console *con);
>  void nbcon_kthread_stop(struct console *con);
>  void nbcon_kthreads_wake(void);
>  
> -/*
> - * Check if the given console is currently capable and allowed to print
> - * records. Note that this function does not consider the current context,
> - * which can also play a role in deciding if @con can be used to print
> - * records.
> - */
> -static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
> -{
> -	if (!(flags & CON_ENABLED))
> -		return false;
> -
> -	if ((flags & CON_SUSPENDED))
> -		return false;
> -
> -	if (flags & CON_NBCON) {
> -		/* The write_atomic() callback is optional. */
> -		if (use_atomic && !con->write_atomic)
> -			return false;
> -
> -		/*
> -		 * For the !use_atomic case, @printk_kthreads_running is not
> -		 * checked because the write_thread() callback is also used
> -		 * via the legacy loop when the printer threads are not
> -		 * available.
> -		 */
> -	} else {
> -		if (!con->write)
> -			return false;
> -	}
> -
> -	/*
> -	 * Console drivers may assume that per-cpu resources have been
> -	 * allocated. So unless they're explicitly marked as being able to
> -	 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
> -	 */
> -	if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
> -		return false;
> -
> -	return true;
> -}
> -
>  /**
>   * nbcon_kthread_wake - Wake up a console printing thread
>   * @con:	Console to operate on
> @@ -204,9 +163,6 @@ static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *hand
>  static inline void nbcon_kthread_wake(struct console *con) { }
>  static inline void nbcon_kthreads_wake(void) { }
>  
> -static inline bool console_is_usable(struct console *con, short flags,
> -				     bool use_atomic) { return false; }
> -
>  #endif /* CONFIG_PRINTK */
>  
>  extern bool have_boot_console;

This also needs the required includes moved over as well. smp.h is
probably more appropriate than the higher level percpu.h:

diff --git a/include/linux/console.h b/include/linux/console.h
index b34c5a0b86303..9406342b27db4 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -19,6 +19,7 @@
 #include <linux/irq_work.h>
 #include <linux/rculist.h>
 #include <linux/rcuwait.h>
+#include <linux/smp.h>
 #include <linux/types.h>
 #include <linux/vesa.h>
 
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 077927ed56c5f..7203b7b969c06 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -3,7 +3,6 @@
  * internal.h - printk internal definitions
  */
 #include <linux/console.h>
-#include <linux/percpu.h>
 #include <linux/types.h>
 
 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)

On a side note, we are missing <linux/rcuwait.h> in
kernel/printk/internal.h. It currently relies on console.h as a
proxy. But I guess that is out of scope for this series.

John