serial: 8250: Defer interrupt enable until fifos enabled

An already-active sender can swamp the interrupt handler with
"too much work" if the rx interrupts are enabled when the fifo is
disabled and operating in single-byte mode.

Defer rx and line status interrupt enable until after the fifos
are enabled in set_termios(), but at least initialize the shadow
IER value with the interrupts which will be enabled.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 4dc143e..de6655d 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2002,12 +2002,11 @@ dont_test_tx_en:
        }
 
        /*
-        * Finally, enable interrupts.  Note: Modem status interrupts
-        * are set via set_termios(), which will be occurring imminently
-        * anyway, so we don't enable them here.
+        * Set the IER shadow for rx interrupts but defer actual interrupt
+        * enable until after the FIFOs are enabled; otherwise, an already-
+        * active sender can swamp the interrupt handler with "too much work".
         */
        up->ier = UART_IER_RLSI | UART_IER_RDI;
-       serial_port_out(port, UART_IER, up->ier);
 
        if (port->flags & UPF_FOURPORT) {
                unsigned int icp;