2022-11-14 16:52:51

by John Ogness

Subject: [PATCH printk v4 35/39] tty: serial: kgdboc: use console_list_lock for list traversal

configure_kgdboc() uses the console_lock for console list iteration. Use
the console_list_lock instead because list synchronization responsibility
will be removed from the console_lock in a later change.

The SRCU iterator could have been used here, but a later change will
relocate the locking of the console_list_lock to also provide
synchronization against register_console().

Note, the console_lock is still needed to serialize the device()
callback with other console operations.

Signed-off-by: John Ogness <[email protected]>
---
drivers/tty/serial/kgdboc.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index c6df9ef34099..82b4b4d67823 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -193,7 +193,16 @@ static int configure_kgdboc(void)
if (!p)
goto noconfig;

+ /* For safe traversal of the console list. */
+ console_list_lock();
+
+ /*
+ * Take console_lock to serialize device() callback with
+ * other console operations. For example, fg_console is
+ * modified under console_lock when switching vt.
+ */
console_lock();
+
for_each_console(cons) {
int idx;
if (cons->device && cons->device(cons, &idx) == p &&
@@ -202,8 +211,11 @@ static int configure_kgdboc(void)
break;
}
}
+
console_unlock();

+ console_list_unlock();
+
kgdb_tty_driver = p;
kgdb_tty_line = tty_line;

--
2.30.2

2022-11-15 16:47:41

by Petr Mladek

Subject: Re: [PATCH printk v4 35/39] tty: serial: kgdboc: use console_list_lock for list traversal

On Mon 2022-11-14 17:35:28, John Ogness wrote:
> configure_kgdboc() uses the console_lock for console list iteration. Use
> the console_list_lock instead because list synchronization responsibility
> will be removed from the console_lock in a later change.
>
> The SRCU iterator could have been used here, but a later change will
> relocate the locking of the console_list_lock to also provide
> synchronization against register_console().
>
> Note, the console_lock is still needed to serialize the device()
> callback with other console operations.
>
> Signed-off-by: John Ogness <[email protected]>

Reviewed-by: Petr Mladek <[email protected]>

Best Regards,
Petr