When unbinding a serial driver, uart_remove_one_port() clears
uart_state.uart_port:
state->uart_port = NULL;
If the serial port is still in use (e.g. by getty), uart_close() will be
called later:
static void uart_close(struct tty_struct *tty, struct file *filp)
{
struct uart_state *state = tty->driver_data;
struct uart_port *uport;
...
if (!state)
return;
uport = state->uart_port;
uport is NULL
...
pr_debug("uart_close(%d) called\n", uport->line);
If debugging is enabled, it will already crash here while dereferencing uport
(this one is easily fixed)
if (tty_port_close_start(port, tty, filp) == 0)
return;
...
uart_flush_buffer(tty);
uart_flush_buffer() will try to obtain the port's spinlock:
static void uart_flush_buffer(struct tty_struct *tty)
{
struct uart_state *state = tty->driver_data;
struct uart_port *port;
...
port = state->uart_port;
port is NULL
...
spin_lock_irqsave(&port->lock, flags);
Crash!!
It doesn't always crash, though.
Sometimes uart_close() returns after the tty_port_close_start() above,
without a crash (bypassing e.g. the call to uart_change_pm() :-(
Sometimes it crashs in uart_chars_in_buffer(), which also tries to take the
spinlock:
tty_port_close_start()
tty_wait_until_sent_from_close()
tty_wait_until_sent()
tty_chars_in_buffer()
uart_chars_in_buffer()
spin_lock_irqsave(&state->uart_port->lock, flags);
I'm not that familiar with the internals of the serial core. Perhaps
uart_close()
should return early if uport is NULL, just like if state is NULL?
However, that means the uart_change_pm(state, UART_PM_STATE_OFF)
is bypassed again.
This is with sh-sci, but I don't think the driver matters.
Thanks for your comments and suggestions!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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