Re: [PATCH v5 3/5] printk: nbcon: Allow KDB to acquire the NBCON context

[John Ogness]

On 2025-09-30, Marcos Paulo de Souza <mpdesouza@xxxxxxxx> wrote:
> diff --git a/include/linux/kdb.h b/include/linux/kdb.h
> index ecbf819deeca118f27e98bf71bb37dd27a257ebb..36b46c85733fe1df28cde7760e5c26e96de40c05 100644
> --- a/include/linux/kdb.h
> +++ b/include/linux/kdb.h
> @@ -207,11 +207,26 @@ static inline const char *kdb_walk_kallsyms(loff_t *pos)
>  /* Dynamic kdb shell command registration */
>  extern int kdb_register(kdbtab_t *cmd);
>  extern void kdb_unregister(kdbtab_t *cmd);
> +
> +/* Return true when KDB as locked for printing a message on this CPU. */
> +static inline
> +bool kdb_printf_on_this_cpu(void)
> +{
> +	/*
> +	 * We can use raw_smp_processor_id() here because the task could
> +	 * not get migrated when KDB has locked for printing on this CPU.
> +	 */
> +	return unlikely(READ_ONCE(kdb_printf_cpu) == raw_smp_processor_id());
> +}
> +
>  #else /* ! CONFIG_KGDB_KDB */
>  static inline __printf(1, 2) int kdb_printf(const char *fmt, ...) { return 0; }
>  static inline void kdb_init(int level) {}
>  static inline int kdb_register(kdbtab_t *cmd) { return 0; }
>  static inline void kdb_unregister(kdbtab_t *cmd) {}
> +
> +static inline bool kdb_printf_on_this_cpu(void) { return false };
> +
>  #endif	/* CONFIG_KGDB_KDB */
>  enum {
>  	KDB_NOT_INITIALIZED,

The include for raw_smp_processor_id() is also needed:

diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index 36b46c85733fe..db9d73b12a1af 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -14,6 +14,7 @@
  */
 
 #include <linux/list.h>
+#include <linux/smp.h>
 
 /* Shifted versions of the command enable bits are be used if the command
  * has no arguments (see kdb_check_flags). This allows commands, such as