From: Serge Semin fancer.lancer@gmail.com
[ Upstream commit 13b18d35909707571af9539f7731389fbf0feb31 ]
A bug was introduced by commit b3b576461864 ("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: b3b576461864 "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 --- drivers/tty/serial/serial_core.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 8dbeb14a1e3a..fe9261ffe3db 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1738,6 +1738,7 @@ 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) @@ -1748,7 +1749,11 @@ 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)