Hi!
Johan Hovold <johan@xxxxxxxxxx> writes:
> 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.
>
Meh, yeah :(
Seem like the correct solution would be to fix start_tx_rs485 and
serial8250_start_tx instead.
Best regards,
Steffen Trumtrar
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