Re: [PATCH 04/19] printk: Reintroduce consoles_suspended global state
From: Petr Mladek <pmladek@suse.com>
Date: 2026-01-14 13:12:24
Also in:
linux-arm-kernel, linux-fsdevel, linux-hardening, linux-m68k, linux-serial, linux-um, lkml, netdev, sparclinux
On Sat 2025-12-27 09:16:11, Marcos Paulo de Souza wrote:
This change partially reverts commit 9e70a5e109a4
("printk: Add per-console suspended state"). The intent of the original
commit was to move the management of the console suspended state to the
consoles themselves to be able to use SRCU instead of console lock.
But having a global state is still useful when checking if the global
suspend was triggered by power management. This way, instead of setting
the state of each individual console, the code would only set/read from the
global state.
Along with this change, two more fixes are necessary: change
console_{suspend,resume} to set/clear CON_SUSPEND instead of setting
CON_ENABLED and change show_cons_active to call __console_is_usable to
check console usefulness.
I would invert the logic a bit. I think that the main motivation
is to replace CON_ENABLE -> CON_SUSPEND.
<proposal>
The flag CON_ENABLE is cleared when serial drivers get suspended. This
"hack" has been added by the commit 33c0d1b0c3ebb6 ("[PATCH] Serial
driver stuff") back in v2.5.28.
Stop hijacking CON_ENABLE flag and use the CON_SUSPEND flag instead.
Still allow to distinguish when:
- the backing device is being suspended, see console_suspend().
- the power management wants to calm down all consoles using
a big-hammer, see console_suspend_all().
And restore the global "consoles_suspended" flag which was removed
by the commit 9e70a5e109a4 ("printk: Add per-console suspended state").
The difference is that accesses to the new global flag are
synchronized the same way as to the CON_SUSPEND flag. It allows
to read it under console_srcu_read_lock().
Finally, use __console_is_usable() in show_cons_active(). It is the
last location where the CON_ENABLED flag was checked directly.
The patch should not change the existing behavior because all users check
the state of the console using console_is_usable().
</proposal>
quoted hunk ↗ jump to hunk
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e2d92cf70eb7..7d2bded75b75 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c@@ -3552,9 +3552,9 @@ static ssize_t show_cons_active(struct device *dev, for_each_console(c) { if (!c->device) continue; - if (!(c->flags & CON_NBCON) && !c->write) - continue; - if ((c->flags & CON_ENABLED) == 0) + if (!__console_is_usable(c, c->flags, + consoles_suspended, + NBCON_USE_ANY))
It would be better to move this into a separate patch.
continue; cs[i++] = c; if (i >= ARRAY_SIZE(cs))
Otherwise, it looks good. Best Regards, Petr