__setup() handlers should return 1 to obsolete_checksetup() in
init/main.c to indicate that the boot option has been handled.
A return of 0 causes the boot option/value to be listed as an Unknown
kernel parameter and added to init's (limited) environment strings.
So return 1 from kgdboc_option_setup().

Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc7
  kgdboc=kbd kgdbts=", will be passed to user space.

 Run /sbin/init as init process
   with arguments:
     /sbin/init
   with environment:
     HOME=/
     TERM=linux
     BOOT_IMAGE=/boot/bzImage-517rc7
     kgdboc=kbd
     kgdbts=

Fixes: 1bd54d851f50 ("kgdboc: Passing ekgdboc to command line causes panic")
Fixes: f2d937f3bf00 ("consoles: polling support, kgdboc")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: He Zhe <zhe.he@windriver.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: kgdb-bugreport@lists.sourceforge.net
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: linux-serial@vger.kernel.org
---
v2- correct Fixes: tag(s) (thanks Doug)
  - drop Cc: Laura Abbott <labbott@redhat.com> (bouncing)
  - add a reference to init/main.c::obsolete_checksetup()

 drivers/tty/serial/kgdboc.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- lnx-517-rc7.orig/drivers/tty/serial/kgdboc.c
+++ lnx-517-rc7/drivers/tty/serial/kgdboc.c
@@ -403,16 +403,16 @@ static int kgdboc_option_setup(char *opt
 {
 	if (!opt) {
 		pr_err("config string not provided\n");
-		return -EINVAL;
+		return 1;
 	}
 
 	if (strlen(opt) >= MAX_CONFIG_LEN) {
 		pr_err("config string too long\n");
-		return -ENOSPC;
+		return 1;
 	}
 	strcpy(config, opt);
 
-	return 0;
+	return 1;
 }
 
 __setup("kgdboc=", kgdboc_option_setup);

Hi,

On Tue, Mar 8, 2022 at 7:30 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> __setup() handlers should return 1 to obsolete_checksetup() in
> init/main.c to indicate that the boot option has been handled.
> A return of 0 causes the boot option/value to be listed as an Unknown
> kernel parameter and added to init's (limited) environment strings.
> So return 1 from kgdboc_option_setup().
>
> Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc7
>   kgdboc=kbd kgdbts=", will be passed to user space.
>
>  Run /sbin/init as init process
>    with arguments:
>      /sbin/init
>    with environment:
>      HOME=/
>      TERM=linux
>      BOOT_IMAGE=/boot/bzImage-517rc7
>      kgdboc=kbd
>      kgdbts=
>
> Fixes: 1bd54d851f50 ("kgdboc: Passing ekgdboc to command line causes panic")
> Fixes: f2d937f3bf00 ("consoles: polling support, kgdboc")
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
> Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
> Cc: He Zhe <zhe.he@windriver.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: kgdb-bugreport@lists.sourceforge.net
> Cc: Jason Wessel <jason.wessel@windriver.com>
> Cc: Daniel Thompson <daniel.thompson@linaro.org>
> Cc: Douglas Anderson <dianders@chromium.org>
> Cc: linux-serial@vger.kernel.org
> ---
> v2- correct Fixes: tag(s) (thanks Doug)
>   - drop Cc: Laura Abbott <labbott@redhat.com> (bouncing)
>   - add a reference to init/main.c::obsolete_checksetup()
>
>  drivers/tty/serial/kgdboc.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Douglas Anderson <dianders@chromium.org>