diff mbox series

[printk,v5,38/40] tty: serial: kgdboc: use console_list_lock to trap exit

Message ID 20221116162152.193147-39-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Nov. 16, 2022, 4:21 p.m. UTC 
  kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
are unregistered until the kgdboc_earlycon is setup. The console_list_lock
should be used instead because list synchronization responsibility will
be removed from the console_lock in a later change.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 drivers/tty/serial/kgdboc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Doug Anderson Nov. 17, 2022, 12:56 a.m. UTC | #1 
Hi,

On Wed, Nov 16, 2022 at 8:22 AM John Ogness <john.ogness@linutronix.de> wrote:
>
> kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
> are unregistered until the kgdboc_earlycon is setup. The console_list_lock
> should be used instead because list synchronization responsibility will
> be removed from the console_lock in a later change.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
>  drivers/tty/serial/kgdboc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 8c2b7ccdfebf..a3ed9b34e2ab 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -558,13 +558,13 @@ static int __init kgdboc_earlycon_init(char *opt)
>          */
>
>         /*
> -        * Hold the console_lock to guarantee that no consoles are
> +        * Hold the console_list_lock to guarantee that no consoles are
>          * unregistered until the kgdboc_earlycon setup is complete.
>          * Trapping the exit() callback relies on exit() not being
>          * called until the trap is setup. This also allows safe
>          * traversal of the console list and race-free reading of @flags.
>          */
> -       console_lock();
> +       console_list_lock();
>         for_each_console(con) {
>                 if (con->write && con->read &&
>                     (con->flags & (CON_BOOT | CON_ENABLED)) &&

Officially don't we need both the list lock and normal lock here since
we're reaching into the consoles?

-Doug
John Ogness Nov. 17, 2022, 11:08 a.m. UTC | #2 
On 2022-11-16, Doug Anderson <dianders@chromium.org> wrote:
>>         /*
>> -        * Hold the console_lock to guarantee that no consoles are
>> +        * Hold the console_list_lock to guarantee that no consoles are
>>          * unregistered until the kgdboc_earlycon setup is complete.
>>          * Trapping the exit() callback relies on exit() not being
>>          * called until the trap is setup. This also allows safe
>>          * traversal of the console list and race-free reading of @flags.
>>          */
>> -       console_lock();
>> +       console_list_lock();
>>         for_each_console(con) {
>>                 if (con->write && con->read &&
>>                     (con->flags & (CON_BOOT | CON_ENABLED)) &&
>
> Officially don't we need both the list lock and normal lock here since
> we're reaching into the consoles?

AFAICT the only synchronization we need here is iterating the console
list, reading con->flags of a registered console, and modifying
con->exit of a registered console. The console_list_lock provides
synchronization for all of these things. By the end of this series the
console_lock does not provide synchronization for any of these things.

Is there something else that requires synchronization here?

After this series the console_lock is still responsible for:

- serializing console->write() callbacks
- stopping console->write() callbacks
- stopping console->device() callbacks
- synchronizing console->seq
- synchronizing console->dropped
- synchronizing the global @console_suspended
- providing various unclear protection for vt consoles
- some bizarre misuses in bcache

The scope may be larger than the above list. The investigation is still
ongoing.

John
diff mbox series

Patch

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 8c2b7ccdfebf..a3ed9b34e2ab 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -558,13 +558,13 @@  static int __init kgdboc_earlycon_init(char *opt)
 	 */
 
 	/*
-	 * Hold the console_lock to guarantee that no consoles are
+	 * Hold the console_list_lock to guarantee that no consoles are
 	 * unregistered until the kgdboc_earlycon setup is complete.
 	 * Trapping the exit() callback relies on exit() not being
 	 * called until the trap is setup. This also allows safe
 	 * traversal of the console list and race-free reading of @flags.
 	 */
-	console_lock();
+	console_list_lock();
 	for_each_console(con) {
 		if (con->write && con->read &&
 		    (con->flags & (CON_BOOT | CON_ENABLED)) &&
@@ -606,7 +606,7 @@  static int __init kgdboc_earlycon_init(char *opt)
 	}
 
 unlock:
-	console_unlock();
+	console_list_unlock();
 
 	/* Non-zero means malformed option so we always return zero */
 	return 0;