On 10/07/2011 11:59 PM, Doug Anderson wrote: > The symptoms of the bug showed up if you were running agetty on ttyS0 > but not using ttyS0 as the console= port on the kernel command > line. In this case, if you suspended the system you'd get a crash > on resume. > > The specific order of operations that were running: > * uart_suspend_port() would be called to put the uart in suspend mode > * a tty hangup would be processed > * the hangup would call uart_shutdown() > * ... suspend / resume happens ... > * uart_resume_port() would be called and run the code in the > (port->flags & ASYNC_SUSPENDED) block, which would startup the port > (and enable tx again). > * Since the UART would be available for tx, we'd immediately get > an interrupt, eventually calling transmit_chars() > * The transmit_chars() function would crash. The first crash would > be a dereference of a NULL tty member, but since the port has been > shutdown that was just a symptom. I cannot reproduce this. What uart driver is this with? And where does it call uart_suspend_port from? Basically, it would mean that it calls uart_suspend_port while userspace is still running? Or who HUPs the port (the second point in your list)? > Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx> > --- > drivers/tty/serial/serial_core.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index a3efbea..668e56a 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -255,6 +255,14 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state) > } > > /* > + * It's possible for shutdown to be called after suspend. Specifically > + * if agetty() is listening to the serial port we get a HUP after the > + * suspend happend (and HUP calls shutdown). Clear suspended bit so > + * we don't try to resume a port that has been shutdown. > + */ > + clear_bit(ASYNCB_SUSPENDED, &port->flags); > + > + /* > * kill off our tasklet > */ > tasklet_kill(&state->tlet); thanks, -- js -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
