diff options
author | Darwin Dingel <darwin.dingel@alliedtelesis.co.nz> | 2018-12-10 11:29:09 +1300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-12-17 16:02:57 +0100 |
commit | 6d7f677a2afa1c82d7fc7af7f9159cbffd5dc010 (patch) | |
tree | 2b38e2d830923e12411591436627eed9aa89d339 /drivers/tty/serial/8250/8250_core.c | |
parent | bdb48e4c7d0796850d4c1a24fe1386677e8a922c (diff) |
serial: 8250: Rate limit serial port rx interrupts during input overruns
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 <darwin.dingel@alliedtelesis.co.nz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/serial/8250/8250_core.c')
-rw-r--r-- | drivers/tty/serial/8250/8250_core.c | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 94f3e1c64490..189ab1212d9a 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -942,6 +942,21 @@ 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; |