From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4EC7C433DF for ; Fri, 5 Jun 2020 09:54:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9523E2075B for ; Fri, 5 Jun 2020 09:54:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726410AbgFEJx7 (ORCPT ); Fri, 5 Jun 2020 05:53:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:58760 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726270AbgFEJx7 (ORCPT ); Fri, 5 Jun 2020 05:53:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 34AA6ACCC; Fri, 5 Jun 2020 09:54:01 +0000 (UTC) Date: Fri, 5 Jun 2020 11:53:56 +0200 From: Petr Mladek To: Sumit Garg Cc: daniel.thompson@linaro.org, kgdb-bugreport@lists.sourceforge.net, jason.wessel@windriver.com, dianders@chromium.org, sergey.senozhatsky@gmail.com, gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 4/4] kdb: Switch to use safer dbg_io_ops over console APIs Message-ID: <20200605095356.GK22497@linux-b0ei> References: <1591264879-25920-1-git-send-email-sumit.garg@linaro.org> <1591264879-25920-5-git-send-email-sumit.garg@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1591264879-25920-5-git-send-email-sumit.garg@linaro.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2020-06-04 15:31:19, Sumit Garg wrote: > In kgdb context, calling console handlers aren't safe due to locks used > in those handlers which could in turn lead to a deadlock. Although, using > oops_in_progress increases the chance to bypass locks in most console > handlers but it might not be sufficient enough in case a console uses > more locks (VT/TTY is good example). > > Currently when a driver provides both polling I/O and a console then kdb > will output using the console. We can increase robustness by using the > currently active polling I/O driver (which should be lockless) instead > of the corresponding console. For several common cases (e.g. an > embedded system with a single serial port that is used both for console > output and debugger I/O) this will result in no console handler being > used. > > In order to achieve this we need to reverse the order of preference to > use dbg_io_ops (uses polling I/O mode) over console APIs. So we just > store "struct console" that represents debugger I/O in dbg_io_ops and > while emitting kdb messages, skip console that matches dbg_io_ops > console in order to avoid duplicate messages. After this change, > "is_console" param becomes redundant and hence removed. > > Suggested-by: Daniel Thompson > Signed-off-by: Sumit Garg Looks good to me now: Reviewed-by: Petr Mladek Best Regards, Petr