2022-11-07 14:23:26

by John Ogness

Subject: [PATCH printk v3 36/40] 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 | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 5be381003e58..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;

@@ -451,6 +463,7 @@ static void kgdboc_earlycon_pre_exp_handler(void)
{
struct console *con;
static bool already_warned;
+ int cookie;

if (already_warned)
return;
@@ -463,9 +476,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
* serial drivers might be OK with this, print a warning once per
* boot if we detect this case.
*/
- for_each_console(con)
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
if (con == kgdboc_earlycon_io_ops.cons)
- return;
+ break;
+ }
+ console_srcu_read_unlock(cookie);
+ if (con)
+ return;

already_warned = true;
pr_warn("kgdboc_earlycon is still using bootconsole\n");
--
2.30.2

2022-11-09 09:30:49

by Daniel Thompson

Subject: Re: [PATCH printk v3 36/40] tty: serial: kgdboc: use console_list_lock for list traversal

On Mon, Nov 07, 2022 at 03:22:34PM +0106, 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]>
> ---
> drivers/tty/serial/kgdboc.c | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 5be381003e58..82b4b4d67823 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -451,6 +463,7 @@ static void kgdboc_earlycon_pre_exp_handler(void)
> {
> struct console *con;
> static bool already_warned;
> + int cookie;
>
> if (already_warned)
> return;
> @@ -463,9 +476,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
> * serial drivers might be OK with this, print a warning once per
> * boot if we detect this case.
> */
> - for_each_console(con)
> + cookie = console_srcu_read_lock();
> + for_each_console_srcu(con) {
> if (con == kgdboc_earlycon_io_ops.cons)
> - return;
> + break;
> + }
> + console_srcu_read_unlock(cookie);
> + if (con)
> + return;

This change isn't mentioned in the patch description.


Daniel.

2022-11-09 10:55:47

by John Ogness

Subject: Re: [PATCH printk v3 36/40] tty: serial: kgdboc: use console_list_lock for list traversal

On 2022-11-09, Daniel Thompson <[email protected]> wrote:
>> @@ -463,9 +476,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
>> * serial drivers might be OK with this, print a warning once per
>> * boot if we detect this case.
>> */
>> - for_each_console(con)
>> + cookie = console_srcu_read_lock();
>> + for_each_console_srcu(con) {
>> if (con == kgdboc_earlycon_io_ops.cons)
>> - return;
>> + break;
>> + }
>> + console_srcu_read_unlock(cookie);
>> + if (con)
>> + return;
>
> This change isn't mentioned in the patch description.

I will move this change into its own separate patch.

tty: serial: kgdboc: use srcu console list iterator

Use srcu console list iteration for safe console list traversal.

Thanks.

John

2022-11-10 18:32:20

by Petr Mladek

Subject: Re: [PATCH printk v3 36/40] tty: serial: kgdboc: use console_list_lock for list traversal

On Wed 2022-11-09 10:50:43, John Ogness wrote:
> On 2022-11-09, Daniel Thompson <[email protected]> wrote:
> >> @@ -463,9 +476,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
> >> * serial drivers might be OK with this, print a warning once per
> >> * boot if we detect this case.
> >> */
> >> - for_each_console(con)
> >> + cookie = console_srcu_read_lock();
> >> + for_each_console_srcu(con) {
> >> if (con == kgdboc_earlycon_io_ops.cons)
> >> - return;
> >> + break;
> >> + }
> >> + console_srcu_read_unlock(cookie);
> >> + if (con)
> >> + return;
> >
> > This change isn't mentioned in the patch description.
>
> I will move this change into its own separate patch.
>
> tty: serial: kgdboc: use srcu console list iterator
>
> Use srcu console list iteration for safe console list traversal.

Yes, split it please :-) Anyway, both changes look good to me.

Best Regards,
Petr