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

John Ogness
2025-06-20T15:45:17Z

On 2025-06-16, Petr Mladek <pmladek@suse.com> wrote:
> 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?

FWIW, I agree with all these points.

John