From 886979da50dec49e2bf9e0627f8875ea7a6d2b53 Mon Sep 17 00:00:00 2001 From: Darwin Dingel Date: Mon, 10 Dec 2018 11:29:09 +1300 Subject: [PATCH] serial: 8250: Rate limit serial port rx interrupts during input overruns BugLink: https://bugs.launchpad.net/bugs/1855787 [ Upstream commit 6d7f677a2afa1c82d7fc7af7f9159cbffd5dc010 ] When a serial port gets faulty or gets flooded with inputs, its interrupt handler starts to work double time to get the characters to the workqueue for the tty layer to handle them. When this busy time on the serial/tty subsystem happens during boot, where it is also busy on the userspace trying to initialise, some processes can continuously get preempted and will be on hold until the interrupts subside. The fix is to backoff on processing received characters for a specified amount of time when an input overrun is seen (received a new character before the previous one is processed). This only stops receive and will continue to transmit characters to serial port. After the backoff period is done, it receive will be re-enabled. This is optional and will only be enabled by setting 'overrun-throttle-ms' in the dts. Signed-off-by: Darwin Dingel Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin Signed-off-by: Kamal Mostafa Signed-off-by: Kleber Sacilotto de Souza --- drivers/tty/serial/8250/8250_core.c | 25 +++++++++++++++++++++++++ drivers/tty/serial/8250/8250_fsl.c | 23 ++++++++++++++++++++++- drivers/tty/serial/8250/8250_of.c | 5 +++++ include/linux/serial_8250.h | 4 ++++ 4 files changed, 56 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 9342fc2ee7df..6840c7d0adc4 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -946,6 +946,21 @@ static struct uart_8250_port *serial8250_find_match_or_unused(struct uart_port * return NULL; } +static void serial_8250_overrun_backoff_work(struct work_struct *work) +{ + struct uart_8250_port *up = + container_of(to_delayed_work(work), struct uart_8250_port, + overrun_backoff); + struct uart_port *port = &up->port; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + up->ier |= UART_IER_RLSI | UART_IER_RDI; + up->port.read_status_mask |= UART_LSR_DR; + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&port->lock, flags); +} + /** * serial8250_register_8250_port - register a serial port * @up: serial port template @@ -1056,6 +1071,16 @@ int serial8250_register_8250_port(struct uart_8250_port *up) ret = 0; } } + + /* Initialise interrupt backoff work if required */ + if (up->overrun_backoff_time_ms > 0) { + uart->overrun_backoff_time_ms = up->overrun_backoff_time_ms; + INIT_DELAYED_WORK(&uart->overrun_backoff, + serial_8250_overrun_backoff_work); + } else { + uart->overrun_backoff_time_ms = 0; + } + mutex_unlock(&serial_mutex); return ret; diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 6640a4c7ddd1..bb9571eed275 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -45,8 +45,29 @@ int fsl8250_handle_irq(struct uart_port *port) lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR); - if (lsr & (UART_LSR_DR | UART_LSR_BI)) + /* Process incoming characters first */ + if ((lsr & (UART_LSR_DR | UART_LSR_BI)) && + (up->ier & (UART_IER_RLSI | UART_IER_RDI))) { lsr = serial8250_rx_chars(up, lsr); + } + + /* Stop processing interrupts on input overrun */ + if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) { + unsigned long delay; + + up->ier = port->serial_in(port, UART_IER); + if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) { + port->ops->stop_rx(port); + } else { + /* Keep restarting the timer until + * the input overrun subsides. + */ + cancel_delayed_work(&up->overrun_backoff); + } + + delay = msecs_to_jiffies(up->overrun_backoff_time_ms); + schedule_delayed_work(&up->overrun_backoff, delay); + } serial8250_modem_status(up); diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c index 4698e0a37f9a..8534408ae39b 100644 --- a/drivers/tty/serial/8250/8250_of.c +++ b/drivers/tty/serial/8250/8250_of.c @@ -227,6 +227,11 @@ static int of_platform_serial_probe(struct platform_device *ofdev) if (of_property_read_bool(ofdev->dev.of_node, "auto-flow-control")) port8250.capabilities |= UART_CAP_AFE; + if (of_property_read_u32(ofdev->dev.of_node, + "overrun-throttle-ms", + &port8250.overrun_backoff_time_ms) != 0) + port8250.overrun_backoff_time_ms = 0; + ret = serial8250_register_8250_port(&port8250); if (ret < 0) goto err_dispose; diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index a27ef5f56431..791a6be0e394 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -134,6 +134,10 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + + /* Serial port overrun backoff */ + struct delayed_work overrun_backoff; + u32 overrun_backoff_time_ms; }; static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up) -- 2.39.2