From: John Ogness Subject: [PATCH 1/3] serial: 8250: unlock port for uart_write_wakeup() Date: Fri, 31 Jul 2015 00:54:21 +0200 Message-ID: <87h9ol2r4y.fsf@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , Tony Lindgren , Peter Hurley , Sebastian Andrzej Siewior , linux-omap@vger.kernel.org, nsekhar@ti.comtony@atomide.com, nm@ti.com, linux-serial@vger.kernel.org List-Id: linux-omap@vger.kernel.org uart_write_wakeup() should be called without holding the port lock. Otherwise a possible recursive spinlock issue can occur, such as the following callchain: 8250_core.c:serial8250_tx_chars() - called with port locked serial_core.c:uart_write_wakeup() tty_io.c:tty_wakeup() st_core.c:st_tty_wakeup() st_core.c:st_tx_wakeup() st_core.c:st_int_write() serial_core.c:uart_write() - locks port Signed-off-by: John Ogness --- drivers/tty/serial/8250/8250_core.c | 6 +++++- drivers/tty/serial/8250/8250_omap.c | 6 +++++- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 37fff12..5ac2425 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -1559,8 +1559,12 @@ void serial8250_tx_chars(struct uart_8250_port *up) } } while (--count > 0); - if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) + if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) { + /* do not hold lock for call to uart_write_wakeup() */ + spin_unlock(&port->lock); uart_write_wakeup(port); + spin_lock(&port->lock); + } DEBUG_INTR("THRE..."); diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index d75a66c..5b39892 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -861,8 +861,12 @@ static void omap_8250_dma_tx_complete(void *param) omap8250_restore_regs(p); } - if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) + if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) { + /* do not hold lock for call to uart_write_wakeup() */ + spin_unlock(&p->port.lock); uart_write_wakeup(&p->port); + spin_lock(&p->port.lock); + } if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port)) { int ret; -- 1.7.10.4