From: Steffen Trumtrar <s.trumtrar@pengutronix.de>
To: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
linux-serial@vger.kernel.org
Subject: Re: [PATCH 1/2] tty: serial: 8250: always call tx_chars under spinlock
Date: Mon, 04 Jan 2021 12:42:06 +0100 [thread overview]
Message-ID: <87eej1dj3l.fsf@pengutronix.de> (raw)
In-Reply-To: <X9CzrUVgyqeuREKK@localhost>
Hi!
Johan Hovold <johan@kernel.org> 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@pengutronix.de>
>> ---
>> 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
--
Pengutronix e.K. | Dipl.-Inform. Steffen Trumtrar |
Steuerwalder Str. 21 | https://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686| Fax: +49-5121-206917-5555 |
next prev parent reply other threads:[~2021-01-04 11:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-09 9:17 [PATCH 1/2] tty: serial: 8250: always call tx_chars under spinlock Steffen Trumtrar
2020-12-09 9:17 ` [PATCH 2/2] tty: serial: 8250: wait till transmitter is empty Steffen Trumtrar
2020-12-09 11:26 ` Johan Hovold
2021-01-04 11:47 ` Steffen Trumtrar
2020-12-09 11:23 ` [PATCH 1/2] tty: serial: 8250: always call tx_chars under spinlock Johan Hovold
2021-01-04 11:42 ` Steffen Trumtrar [this message]
[not found] ` <87ft3hdj3n.fsf@pengutronix.de>
2021-01-05 7:33 ` Steffen Trumtrar
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