Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752387AbbG3Wya (ORCPT ); Thu, 30 Jul 2015 18:54:30 -0400 Received: from www.linutronix.de ([62.245.132.108]:48974 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905AbbG3Wy2 (ORCPT ); Thu, 30 Jul 2015 18:54:28 -0400 From: John Ogness To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman Cc: Tony Lindgren Cc: Peter Hurley Cc: Sebastian Andrzej Siewior Cc: linux-omap@vger.kernel.org Cc: nsekhar@ti.com Cc: tony@atomide.com Cc: nm@ti.com Cc: linux-serial@vger.kernel.org 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> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2117 Lines: 61 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/