On Wed, Dec 09, 2020 at 10:17:27AM +0100, Steffen Trumtrar wrote:
> In most cases serial8250_tx_chars is called with spinlock held.
> Fix the remaining location, too.
Please explain where __start_tx() is called without holding the port
lock and consider fixing that up.
> Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_port.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index b0af13074cd3..3310c2b70138 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1559,6 +1559,7 @@ static void serial8250_stop_tx(struct uart_port *port)
> static inline void __start_tx(struct uart_port *port)
> {
> struct uart_8250_port *up = up_to_u8250p(port);
> + unsigned long flags;
>
> if (up->dma && !up->dma->tx_dma(up))
> return;
> @@ -1569,8 +1570,11 @@ static inline void __start_tx(struct uart_port *port)
>
> lsr = serial_in(up, UART_LSR);
> up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
> - if (lsr & UART_LSR_THRE)
> + if (lsr & UART_LSR_THRE) {
> + spin_lock_irqsave(&port->lock, flags);
> serial8250_tx_chars(up);
> + spin_unlock_irqrestore(&port->lock, flags);
> + }
Since several callers of __start_tx() do hold the lock, this change will
introduce a deadlock.
> }
> }
Johan
