Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754498AbbFEKJm (ORCPT ); Fri, 5 Jun 2015 06:09:42 -0400 Received: from TYO200.gate.nec.co.jp ([210.143.35.50]:60597 "EHLO tyo200.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751149AbbFEKJi (ORCPT ); Fri, 5 Jun 2015 06:09:38 -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 0/2] serial: 8250: Workaround to avoid irq=0 for console Thread-Topic: [PATCH 0/2] serial: 8250: Workaround to avoid irq=0 for console Thread-Index: AQHQn3XM4Pt7XBRbREauQ4fcrjoxhw== Date: Fri, 5 Jun 2015 09:55:48 +0000 Message-ID: <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 t55A9mUa009980 Content-Length: 2161 Lines: 49 This patch set provides a workaround to avoid the following problem. It's based on Linux 4.1-rc3 mainstream kernel. I've tested this patch set on x86-64 machine and KVM. Problem -------------------------- There're cases where autoconfig_irq() fails during boot. In these cases, 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. I saw the original problem on RHEL6.6. Fix -------------------------- serial: 8250: Fix autoconfig_irq() to avoid race conditions Fix one of autoconfig_irq() failure case. serial: 8250: Allow to skip autoconfig_irq() for a console Provide a workaround to avoid other autoconfig_irq() failure cases. Conditions of Reproduction -------------------------- - Build with CONFIG_SERIAL_8250_DETECT_IRQ. - Need non-PnP console serial or PnP console with no CONFIG_SERIAL_8250_PNP - Kick printk() repeatedly on the CPU which can handle an interrupt from a console serial during autoconfig_irq(). The CPU is basically cpu0. - Disable the interrupt of the CPU for longer during autoconfig_irq(). Note -------------------------- Ideally, I think autoconfig_irq() should be fixed completely, but it's hard from the following points as long as auto_irq algorithm is used. - How long it should wait for an interrrupt - How to assure the interrupt of the CPU enabled during auto_irq - How to know which CPU can handle an interrupt from a serial. Do you have any other idea? In my opinion, providing a workaround is better than applying big changes to the old function for legacy devices. Taichi Kageyama (2): serial: 8250: Fix autoconfig_irq() to avoid race conditions serial: 8250: Allow to skip autoconfig_irq() for a console drivers/tty/serial/8250/8250_core.c | 23 +++++++++++++++++++++++ 1 files changed, 23 insertions(+), 0 deletions(-) ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?