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/kgdboc.c | 20 +++++--------------- drivers/tty/serial/serial_core.c | 5 +++++ kernel/printk/printk.c | 1 + 3 files changed, 11 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); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 9ec101766471..3f7c8ed96512 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -123,6 +123,7 @@ bool console_srcu_read_lock_is_held(void) { return srcu_read_lock_held(&console_srcu); } +EXPORT_SYMBOL(console_srcu_read_lock_is_held); #endif enum devkmsg_log_bits { -- cgit v1.2.3 From 4fe59a130c112460626a6a8b9232aa580d9b8efc Mon Sep 17 00:00:00 2001 From: Anuradha Weeraman Date: Mon, 16 Jan 2023 18:26:34 +0530 Subject: kernel/printk/printk.c: Fix W=1 kernel-doc warning Fix W=1 kernel-doc warning: kernel/printk/printk.c: - Include function parameter in console_lock_spinning_disable_and_check() Signed-off-by: Anuradha Weeraman Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230116125635.374567-1-anuradha@debian.org --- kernel/printk/printk.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 3f7c8ed96512..39221b0f918d 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1892,6 +1892,7 @@ static void console_lock_spinning_enable(void) /** * console_lock_spinning_disable_and_check - mark end of code where another * thread was able to busy wait and check if there is a waiter + * @cookie: cookie returned from console_srcu_read_lock() * * This is called at the end of the section where spinning is allowed. * It has two functions. First, it is a signal that it is no longer -- cgit v1.2.3