Re: [PATCH 5/7] arch: um: kmsg_dump: Don't check for CON_ENABLED

Petr Mladek
2025-06-16T13:33:31Z

On Fri 2025-06-06 23:53:47, Marcos Paulo de Souza wrote:
> All consoles found on for_each_console are registered, meaning that all of
> them are CON_ENABLED. The code tries to find an active console, so check if the
> console is not suspended instead.
>
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---
> arch/um/kernel/kmsg_dump.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 4190211752726593dd2847f66efd9d3a61cea982..f3025b2a813453f479d720618c630bee135d4e08 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -31,7 +31,7 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> * expected to output the crash information.
> */
> if (strcmp(con->name, "ttynull") != 0 &&
> - (console_srcu_read_flags(con) & CON_ENABLED)) {
> + (console_srcu_read_flags(con) & CON_SUSPENDED) == 0) {
> break;

I think that we should actually replace the check of the
CON_ENABLE/CON_SUSPENDED flag with

is_console_usable(con, console_srcu_read_flags(con), true)

And it should be done at the beginning of the patchset before
changing the semantic of the flags.

Motivation:

There is the following comment at the beginning of the function:

/*
* If no consoles are available to output crash information, dump
* the kmsg buffer to stdout.
*/

The if-condition checks for:

+ "ttynull" because this special console does not show any messages
by definition

+ disabled/suspended consoles; note that this patchset is replacing
CON_ENABLED with CON_SUSPENDED flag because it the state is
changed during suspend.

But it should check also for:

+ whether the console is NBCON_console and does not have con->write_atomic
because such a console would not be able to show the messages
in panic().

And it should also check the global "consoles_suspended" flag. Because
consoles won't show anything when it is set.

And all these is already done by "is_console_usable()" except for
the check of "ttynull" which is very special.

How does the sound, please?

Best Regards,
Petr

> }
> }
>
> --
> 2.49.0