Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754286AbbGWWcF (ORCPT ); Thu, 23 Jul 2015 18:32:05 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46283 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753977AbbGWWcD (ORCPT ); Thu, 23 Jul 2015 18:32:03 -0400 Date: Thu, 23 Jul 2015 15:32:02 -0700 From: "gregkh@linuxfoundation.org" To: Taichi Kageyama Cc: "linux-serial@vger.kernel.org" , "jslaby@suse.cz" , "linux-kernel@vger.kernel.org" , "prarit@redhat.com" , Naoya Horiguchi Subject: Re: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race conditions Message-ID: <20150723223202.GA23915@kroah.com> References: <55717224.9060104@cp.jp.nec.com> <55717294.8020905@cp.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55717294.8020905@cp.jp.nec.com> User-Agent: Mutt/1.5.23+102 (2ca89bed6448) (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1962 Lines: 39 On Fri, Jun 05, 2015 at 09:57:40AM +0000, Taichi Kageyama wrote: > 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 > Reviewed-by: Peter Hurley > --- > drivers/tty/serial/8250/8250_core.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) Does not apply to 4.2-rc3 :( -- 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/