Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932627AbbFEKLd (ORCPT ); Fri, 5 Jun 2015 06:11:33 -0400 Received: from TYO200.gate.nec.co.jp ([210.143.35.50]:60622 "EHLO tyo200.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754211AbbFEKK1 (ORCPT ); Fri, 5 Jun 2015 06:10:27 -0400 From: Taichi Kageyama To: "gregkh@linuxfoundation.org" CC: "linux-serial@vger.kernel.org" , "jslaby@suse.cz" , "linux-kernel@vger.kernel.org" , "prarit@redhat.com" , Naoya Horiguchi Subject: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race conditions Thread-Topic: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race conditions Thread-Index: AQHQn3YPfR1JLIP5kUuZc3LH0ejwmg== Date: Fri, 5 Jun 2015 09:57:40 +0000 Message-ID: <55717294.8020905@cp.jp.nec.com> References: <55717224.9060104@cp.jp.nec.com> In-Reply-To: <55717224.9060104@cp.jp.nec.com> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.34.108.73] Content-Type: text/plain; charset="utf-8" Content-ID: MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id t55ABcvJ010007 Content-Length: 2373 Lines: 59 The following race conditions can happen if a serial is used as console. Case1. CPU_B handles an interrupt from a serial autoconfig_irq() fails whether the interrupt is raised or not if CPU_B is disabled to handle interrupts for longer than it expects. Case2. CPU_B clears UART_IER just after CPU_A sets UART_IER A serial may not make an interrupt. autoconfig_irq() can fail if the interrupt is not raised. Case3. CPU_A sets UART_IER just after CPU_B clears UART_IER This is an unexpected behavior for uart_console_write(). CPU_A [autoconfig_irq] CPU_B [serial8250_console_write] ----------------------------------------------------------------- probe_irq_on() spin_lock_irqsave(&port->lock,) serial_outp(,UART_IER,0x0f) serial_out(,UART_IER,0) udelay(20); uart_console_write() probe_irq_off() spin_unlock_irqrestore(&port->lock,) ----------------------------------------------------------------- If autoconfig_irq() fails, the console doesn't work in interrupt mode, the mode cannot be changed anymore, and "input overrun" (which can make operation mistakes) happens easily. This problem happens with high rate every boot once it occurs because the boot sequence is always almost same. Signed-off-by: Taichi Kageyama Cc: Naoya Horiguchi --- drivers/tty/serial/8250/8250_core.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 4506e40..6bf31f2 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -1309,6 +1309,9 @@ static void autoconfig_irq(struct uart_8250_port *up) unsigned long irqs; int irq; + if (uart_console(port)) + console_lock(); + if (port->flags & UPF_FOURPORT) { ICP = (port->iobase & 0xfe0) | 0x1f; save_ICP = inb_p(ICP); @@ -1347,6 +1350,9 @@ static void autoconfig_irq(struct uart_8250_port *up) if (port->flags & UPF_FOURPORT) outb_p(save_ICP, ICP); + if (uart_console(port)) + console_unlock(); + port->irq = (irq > 0) ? irq : 0; } -- 1.7.1 ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?