On Mon, Nov 01, 2021 at 05:48:08PM +0200, Baruch Siach wrote: > When a signal interrupts tty_wait_until_sent() on a UART device, there > might be data left on the xmit buffer that the UART will never transmit. > This causes set_termios() to wait forever in tty_wait_until_sent(). > > The hang reproduces easily on my system that is equipped with DesignWare > 8250. Run > > while true; do echo -ne 0123456789abcdef01 > /dev/ttyS1; done > > Hit Ctrl-C to interrupt the loop. When data is left in the struct > uart_state xmit buffer, the following command hangs: > > stty -F /dev/ttyS1 raw -echo Thanks for reporting this. It should not be possible for there to be data left in the buffer and indeed we do have a long-standing regression here since the serdev work five years ago. I'm a bit surprised no one has noticed and reported this for that long. > Call tty_driver_flush_buffer() on signal interrupted wait, to discard > data from the xmit buffer. > > Signed-off-by: Baruch Siach <baruch@xxxxxxxxxx> > --- > drivers/tty/tty_ioctl.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c > index 507a25d692bb..0bf6fad7ecb3 100644 > --- a/drivers/tty/tty_ioctl.c > +++ b/drivers/tty/tty_ioctl.c > @@ -203,6 +203,8 @@ void tty_wait_until_sent(struct tty_struct *tty, long timeout) > > timeout = wait_event_interruptible_timeout(tty->write_wait, > !tty_chars_in_buffer(tty), timeout); > + if (timeout == -ERESTARTSYS && tty->closing) > + tty_driver_flush_buffer(tty); > if (timeout <= 0) > return; This is however not the right fix since the problem isn't limited to interrupted waits and in any case should not be handled in tty_wait_until_sent(). I can reproduce the problem and have posted a fix here: https://lore.kernel.org/r/20211108083856.5261-1-johan@xxxxxxxxxx Johan
