diff options
author | John Ogness <john.ogness@linutronix.de> | 2023-01-12 19:12:13 +0300 |
---|---|---|
committer | Petr Mladek <pmladek@suse.com> | 2023-01-16 18:44:53 +0300 |
commit | 3ef5abd9b5c738bc6fa9a65e40331ef2cb03ad9c (patch) | |
tree | 304c478b077057aff9a335cf416483b187da2cab /drivers/tty | |
parent | 5074ffbec67ac592614901771d3a15e1198d759d (diff) | |
download | linux-3ef5abd9b5c738bc6fa9a65e40331ef2cb03ad9c.tar.xz |
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 <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
[pmladek@suse.com: Export console_srcu_read_lock_is_held() to fix build kgdboc as a module.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230112161213.1434854-1-john.ogness@linutronix.de
Diffstat (limited to 'drivers/tty')
-rw-r--r-- | drivers/tty/serial/kgdboc.c | 20 | ||||
-rw-r--r-- | 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); |