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Message-ID: <84ecrmhdci.fsf@jogness.linutronix.de>
Date: Wed, 01 Oct 2025 17:11:17 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Marcos Paulo de Souza <mpdesouza@...e.com>, Greg Kroah-Hartman
<gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, Steven
Rostedt <rostedt@...dmis.org>, Sergey Senozhatsky
<senozhatsky@...omium.org>, Jason Wessel <jason.wessel@...driver.com>,
Daniel Thompson <danielt@...nel.org>, Douglas Anderson
<dianders@...omium.org>
Cc: linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
Marcos Paulo de Souza <mpdesouza@...e.com>
Subject: Re: [PATCH v5 3/5] printk: nbcon: Allow KDB to acquire the NBCON
context
On 2025-09-30, Marcos Paulo de Souza <mpdesouza@...e.com> 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
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