@@ -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;
@@ -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);
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 <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> --- drivers/tty/serial/kgdboc.c | 20 +++++--------------- drivers/tty/serial/serial_core.c | 5 +++++ 2 files changed, 10 insertions(+), 15 deletions(-) base-commit: b7bfaa761d760e72a969d116517eaa12e404c262