Commit 47807595 authored May 08, 2019 by Serge Semin Committed by Greg Kroah-Hartman Aug 04, 2019

tty: serial_core: Set port active bit in uart_port_activate



[ Upstream commit 13b18d35909707571af9539f7731389fbf0feb31 ]

A bug was introduced by commit b3b57646 ("tty: serial_core: convert
uart_open to use tty_port_open"). It caused a constant warning printed
into the system log regarding the tty and port counter mismatch:

[   21.644197] ttyS ttySx: tty_port_close_start: tty->count = 1 port count = 2

in case if session hangup was detected so the warning is printed starting
from the second open-close iteration.

Particularly the problem was discovered in situation when there is a
serial tty device without hardware back-end being setup. It is considered
by the tty-serial subsystems as a hardware problem with session hang up.
In this case uart_startup() will return a positive value with TTY_IO_ERROR
flag set in corresponding tty_struct instance. The same value will get
passed to be returned from the activate() callback and then being returned
from tty_port_open(). But since in this case tty_port_block_til_ready()
isn't called the TTY_PORT_ACTIVE flag isn't set (while the method had been
called before tty_port_open conversion was introduced and the rest of the
subsystem code expected the bit being set in this case), which prevents the
uart_hangup() method to perform any cleanups including the tty port
counter setting to zero. So the next attempt to open/close the tty device
will discover the counters mismatch.

In order to fix the problem we need to manually set the TTY_PORT_ACTIVE
flag in case if uart_startup() returned a positive value. In this case
the hang up procedure will perform a full set of cleanup actions including
the port ref-counter resetting.

Fixes: b3b57646 "tty: serial_core: convert uart_open to use tty_port_open"
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 1d133532

drivers/tty/serial/serial_core.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1725,6 +1725,7 @@ static int uart_port_activate(struct tty_port port, struct tty_struct tty)
		{
		struct uart_state *state = container_of(port, struct uart_state, port);
		struct uart_port *uport;
		int ret;

		uport = uart_port_check(state);
		if (!uport \|\| uport->flags & UPF_DEAD)
		@@ -1735,7 +1736,11 @@ static int uart_port_activate(struct tty_port port, struct tty_struct tty)
		/*
		* Start up the serial port.
		*/
		return uart_startup(tty, state, 0);
		ret = uart_startup(tty, state, 0);
		if (ret > 0)
		tty_port_set_active(port, 1);

		return ret;
		}

		static const char uart_type(struct uart_port port)