Several mutexes are taken while setting up console serial ports. In
particular, the tty_port->mutex and @console_mutex are taken:
serial_pnp_probe
serial8250_register_8250_port
uart_add_one_port (locks tty_port->mutex)
uart_configure_port
register_console (locks @console_mutex)
In order to synchronize kgdb's tty_find_polling_driver() with
register_console(), commit 6193bc90849a ("tty: serial: kgdboc:
synchronize tty_find_polling_driver() and register_console()") takes
the @console_mutex. However, this leads to the following call chain
(with locking):
platform_probe
kgdboc_probe
configure_kgdboc (locks @console_mutex)
tty_find_polling_driver
uart_poll_init (locks tty_port->mutex)
uart_set_options
This is clearly deadlock potential due to the reverse lock ordering.
Since uart_set_options() requires holding @console_mutex in order to
serialize early initialization of the serial-console lock, take the
@console_mutex in uart_poll_init() instead of configure_kgdboc().
Since configure_kgdboc() was using @console_mutex for safe traversal
of the console list, change it to use the SRCU iterator instead.
Add comments to uart_set_options() kerneldoc mentioning that it
requires holding @console_mutex (aka the console_list_lock).
Fixes: 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()")
Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
---
drivers/tty/serial/kgdboc.c | 20 +++++---------------
drivers/tty/serial/serial_core.c | 5 +++++
2 files changed, 10 insertions(+), 15 deletions(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index a3ed9b34e2ab..7ce7bb164005 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -171,6 +171,7 @@ static int configure_kgdboc(void)
int err = -ENODEV;
char *cptr = config;
struct console *cons;
+ int cookie;
if (!strlen(config) || isspace(config[0])) {
err = 0;
@@ -189,20 +190,9 @@ static int configure_kgdboc(void)
if (kgdboc_register_kbd(&cptr))
goto do_register;
- /*
- * tty_find_polling_driver() can call uart_set_options()
- * (via poll_init) to configure the uart. Take the console_list_lock
- * in order to synchronize against register_console(), which can also
- * configure the uart via uart_set_options(). This also allows safe
- * traversal of the console list.
- */
- console_list_lock();
-
p = tty_find_polling_driver(cptr, &tty_line);
- if (!p) {
- console_list_unlock();
+ if (!p)
goto noconfig;
- }
/*
* Take console_lock to serialize device() callback with
@@ -211,7 +201,8 @@ static int configure_kgdboc(void)
*/
console_lock();
- for_each_console(cons) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(cons) {
int idx;
if (cons->device && cons->device(cons, &idx) == p &&
idx == tty_line) {
@@ -219,11 +210,10 @@ static int configure_kgdboc(void)
break;
}
}
+ console_srcu_read_unlock(cookie);
console_unlock();
- console_list_unlock();
-
kgdb_tty_driver = p;
kgdb_tty_line = tty_line;
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index b9fbbee598b8..ec874f3a567c 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2212,6 +2212,9 @@ EXPORT_SYMBOL_GPL(uart_parse_options);
* @parity: parity character - 'n' (none), 'o' (odd), 'e' (even)
* @bits: number of data bits
* @flow: flow control character - 'r' (rts)
+ *
+ * Locking: Caller must hold console_list_lock in order to serialize
+ * early initialization of the serial-console lock.
*/
int
uart_set_options(struct uart_port *port, struct console *co,
@@ -2619,7 +2622,9 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
if (!ret && options) {
uart_parse_options(options, &baud, &parity, &bits, &flow);
+ console_list_lock();
ret = uart_set_options(port, NULL, baud, parity, bits, flow);
+ console_list_unlock();
}
out:
mutex_unlock(&tport->mutex);
base-commit: b7bfaa761d760e72a969d116517eaa12e404c262
--
2.30.2
On Thu 2023-01-12 17:18:13, John Ogness wrote:
> Several mutexes are taken while setting up console serial ports. In
> particular, the tty_port->mutex and @console_mutex are taken:
>
> serial_pnp_probe
> serial8250_register_8250_port
> uart_add_one_port (locks tty_port->mutex)
> uart_configure_port
> register_console (locks @console_mutex)
>
> In order to synchronize kgdb's tty_find_polling_driver() with
> register_console(), commit 6193bc90849a ("tty: serial: kgdboc:
> synchronize tty_find_polling_driver() and register_console()") takes
> the @console_mutex. However, this leads to the following call chain
> (with locking):
>
> platform_probe
> kgdboc_probe
> configure_kgdboc (locks @console_mutex)
> tty_find_polling_driver
> uart_poll_init (locks tty_port->mutex)
> uart_set_options
>
> This is clearly deadlock potential due to the reverse lock ordering.
>
> Since uart_set_options() requires holding @console_mutex in order to
> serialize early initialization of the serial-console lock, take the
> @console_mutex in uart_poll_init() instead of configure_kgdboc().
>
> Since configure_kgdboc() was using @console_mutex for safe traversal
> of the console list, change it to use the SRCU iterator instead.
>
> Add comments to uart_set_options() kerneldoc mentioning that it
> requires holding @console_mutex (aka the console_list_lock).
>
> Fixes: 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()")
> Signed-off-by: John Ogness <[email protected]>
> Reviewed-by: Petr Mladek <[email protected]>
JFYI, the patch has been committed into printk/linux.git,
branch rework/console-list-lock.
I am going to give it few days in linux-next. If there is no problem
I will send a pull request for 6.2-rc5 later the following week.
Please, let me known if you have another preference.
Best Regards,
Petr
On 2023-01-13, Petr Mladek <[email protected]> wrote:
> JFYI, the patch has been committed into printk/linux.git,
> branch rework/console-list-lock.
Thanks!
> I am going to give it few days in linux-next. If there is no problem
> I will send a pull request for 6.2-rc5 later the following week.
Sounds good to me. For the 6.2 pull request, please also add Sergey's
reviewed-by tag.
John Ogness
On Fri 2023-01-13 10:38:24, John Ogness wrote:
> On 2023-01-13, Petr Mladek <[email protected]> wrote:
> > JFYI, the patch has been committed into printk/linux.git,
> > branch rework/console-list-lock.
>
> > I am going to give it few days in linux-next. If there is no problem
> > I will send a pull request for 6.2-rc5 later the following week.
>
> Sounds good to me. For the 6.2 pull request, please also add Sergey's
> reviewed-by tag.
Done. Sigh, I have missed it in the original commit. I am somehow in
rush last three days and "b4" script did not get it.
Best Regards,
Petr