| Message ID | 20210416140557.25177-3-johan@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | serial: sysrq cleanup and stm32 fixes | expand |
On Fri, Apr 16, 2021 at 04:05:56PM +0200, Johan Hovold wrote: > When DMA is enabled the receive handler runs in a threaded handler, but > the primary handler up until very recently neither disabled interrupts Scratch the "up until very recently" bit here since the driver still doesn't disable interrupt in the device (it just disables all interrupts in the threaded handler). The rest stands as is. > in the device or used IRQF_ONESHOT. This would lead to a deadlock if an > interrupt comes in while the threaded receive handler is running under > the port lock. > > Commit ad7676812437 ("serial: stm32: fix a deadlock condition with > wakeup event") claimed to fix an unrelated deadlock, but unfortunately > also disabled interrupts in the threaded handler. While this prevents > the deadlock mentioned in the previous paragraph it also defeats the > purpose of using a threaded handler in the first place. > > Fix this by making the interrupt one-shot and not disabling interrupts > in the threaded handler. > > Note that (receive) DMA must not be used for a console port as the > threaded handler could be interrupted while holding the port lock, > something which could lead to a deadlock in case an interrupt handler > ends up calling printk. Johan
Hi, Johan On 4/16/21 4:05 PM, Johan Hovold wrote: > When DMA is enabled the receive handler runs in a threaded handler, but > the primary handler up until very recently neither disabled interrupts > in the device or used IRQF_ONESHOT. This would lead to a deadlock if an > interrupt comes in while the threaded receive handler is running under > the port lock. > > Commit ad7676812437 ("serial: stm32: fix a deadlock condition with > wakeup event") claimed to fix an unrelated deadlock, but unfortunately > also disabled interrupts in the threaded handler. While this prevents > the deadlock mentioned in the previous paragraph it also defeats the > purpose of using a threaded handler in the first place. > > Fix this by making the interrupt one-shot and not disabling interrupts > in the threaded handler. > > Note that (receive) DMA must not be used for a console port as the > threaded handler could be interrupted while holding the port lock, > something which could lead to a deadlock in case an interrupt handler > ends up calling printk. > > Fixes: ad7676812437 ("serial: stm32: fix a deadlock condition with wakeup event") > Fixes: 3489187204eb ("serial: stm32: adding dma support") > Cc: stable@vger.kernel.org # 4.9 > Cc: Alexandre TORGUE <alexandre.torgue@st.com> > Cc: Gerald Baeza <gerald.baeza@st.com> > Signed-off-by: Johan Hovold <johan@kernel.org> Reviewed-by: Valentin Caron<valentin.caron@foss.st.com> > --- > drivers/tty/serial/stm32-usart.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) > > diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c > index 4d277804c63e..3524ed2c0c73 100644 > --- a/drivers/tty/serial/stm32-usart.c > +++ b/drivers/tty/serial/stm32-usart.c > @@ -214,14 +214,11 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded) > struct tty_port *tport = &port->state->port; > struct stm32_port *stm32_port = to_stm32_port(port); > const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs; > - unsigned long c, flags; > + unsigned long c; > u32 sr; > char flag; > > - if (threaded) > - spin_lock_irqsave(&port->lock, flags); > - else > - spin_lock(&port->lock); > + spin_lock(&port->lock); > > while (stm32_usart_pending_rx(port, &sr, &stm32_port->last_res, > threaded)) { > @@ -278,10 +275,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded) > uart_insert_char(port, sr, USART_SR_ORE, c, flag); > } > > - if (threaded) > - spin_unlock_irqrestore(&port->lock, flags); > - else > - spin_unlock(&port->lock); > + spin_unlock(&port->lock); > > tty_flip_buffer_push(tport); > } > @@ -667,7 +661,8 @@ static int stm32_usart_startup(struct uart_port *port) > > ret = request_threaded_irq(port->irq, stm32_usart_interrupt, > stm32_usart_threaded_interrupt, > - IRQF_NO_SUSPEND, name, port); > + IRQF_ONESHOT | IRQF_NO_SUSPEND, > + name, port); > if (ret) > return ret; > > @@ -1156,6 +1151,13 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port, > struct dma_async_tx_descriptor *desc = NULL; > int ret; > > + /* > + * Using DMA and threaded handler for the console could lead to > + * deadlocks. > + */ > + if (uart_console(port)) > + return -ENODEV; > + > /* Request DMA RX channel */ > stm32port->rx_ch = dma_request_slave_channel(dev, "rx"); > if (!stm32port->rx_ch) {
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c index 4d277804c63e..3524ed2c0c73 100644 --- a/drivers/tty/serial/stm32-usart.c +++ b/drivers/tty/serial/stm32-usart.c @@ -214,14 +214,11 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded) struct tty_port *tport = &port->state->port; struct stm32_port *stm32_port = to_stm32_port(port); const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs; - unsigned long c, flags; + unsigned long c; u32 sr; char flag; - if (threaded) - spin_lock_irqsave(&port->lock, flags); - else - spin_lock(&port->lock); + spin_lock(&port->lock); while (stm32_usart_pending_rx(port, &sr, &stm32_port->last_res, threaded)) { @@ -278,10 +275,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded) uart_insert_char(port, sr, USART_SR_ORE, c, flag); } - if (threaded) - spin_unlock_irqrestore(&port->lock, flags); - else - spin_unlock(&port->lock); + spin_unlock(&port->lock); tty_flip_buffer_push(tport); } @@ -667,7 +661,8 @@ static int stm32_usart_startup(struct uart_port *port) ret = request_threaded_irq(port->irq, stm32_usart_interrupt, stm32_usart_threaded_interrupt, - IRQF_NO_SUSPEND, name, port); + IRQF_ONESHOT | IRQF_NO_SUSPEND, + name, port); if (ret) return ret; @@ -1156,6 +1151,13 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port, struct dma_async_tx_descriptor *desc = NULL; int ret; + /* + * Using DMA and threaded handler for the console could lead to + * deadlocks. + */ + if (uart_console(port)) + return -ENODEV; + /* Request DMA RX channel */ stm32port->rx_ch = dma_request_slave_channel(dev, "rx"); if (!stm32port->rx_ch) {
When DMA is enabled the receive handler runs in a threaded handler, but the primary handler up until very recently neither disabled interrupts in the device or used IRQF_ONESHOT. This would lead to a deadlock if an interrupt comes in while the threaded receive handler is running under the port lock. Commit ad7676812437 ("serial: stm32: fix a deadlock condition with wakeup event") claimed to fix an unrelated deadlock, but unfortunately also disabled interrupts in the threaded handler. While this prevents the deadlock mentioned in the previous paragraph it also defeats the purpose of using a threaded handler in the first place. Fix this by making the interrupt one-shot and not disabling interrupts in the threaded handler. Note that (receive) DMA must not be used for a console port as the threaded handler could be interrupted while holding the port lock, something which could lead to a deadlock in case an interrupt handler ends up calling printk. Fixes: ad7676812437 ("serial: stm32: fix a deadlock condition with wakeup event") Fixes: 3489187204eb ("serial: stm32: adding dma support") Cc: stable@vger.kernel.org # 4.9 Cc: Alexandre TORGUE <alexandre.torgue@st.com> Cc: Gerald Baeza <gerald.baeza@st.com> Signed-off-by: Johan Hovold <johan@kernel.org> --- drivers/tty/serial/stm32-usart.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)