From 3ef5abd9b5c738bc6fa9a65e40331ef2cb03ad9c Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 12 Jan 2023 17:18:13 +0106 Subject: tty: serial: kgdboc: fix mutex locking order for configure_kgdboc() 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 Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek [pmladek@suse.com: Export console_srcu_read_lock_is_held() to fix build kgdboc as a module.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230112161213.1434854-1-john.ogness@linutronix.de --- drivers/tty/serial/serial_core.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'drivers/tty/serial/serial_core.c') 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); -- cgit v1.2.3