Re: [PATCH 6/7] debug: kgd_io: Don't check for CON_ENABLED

Petr Mladek
2025-06-16T13:57:16Z

On Fri 2025-06-06 23:53:48, Marcos Paulo de Souza wrote:
> All consoles found on for_each_console_srcu 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>
> ---
> kernel/debug/kdb/kdb_io.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 9b11b10b120cf07e451a7a4d92ce50f9a6c066b2..cdc1ee81d7332a9a00b967af719939f438f26cef 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -589,7 +589,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
> */
> cookie = console_srcu_read_lock();
> for_each_console_srcu(c) {
> - if (!(console_srcu_read_flags(c) & CON_ENABLED))
> + if (console_srcu_read_flags(c) & CON_SUSPENDED)
> continue;

I think that this is similar to the 5th patch. We should check
here is_console_usable(con, console_srcu_read_flags(c), true)
because it checks more conditions:

+ the global console_suspended flag. The consoles drivers should
not be used when it is set...

+ whether NBCON console driver has con->write_atomic

and we should also fix kdb_msg_write() to actually use
con->write_atomic() when it is a NBCON console driver.
There is hard-coded con->write() at the moment.

But it might get more complicated. It would be nice to do it correctly
and use con->write_atomit() only when nbcon_context_try_acquire()
succeeds. We probably should use a context with NBCON_PRIO_EMERGENCY.

And this should be fixed at the beginning of the patchset because
it actually fixes the support of the new NBCON console drivers.

Best Regards,
Petr

> if (c == dbg_io_ops->cons)
> continue;
>
> --
> 2.49.0