From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757769AbcEEQnP (ORCPT ); Thu, 5 May 2016 12:43:15 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:45393 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756834AbcEEQnO (ORCPT ); Thu, 5 May 2016 12:43:14 -0400 Date: Thu, 5 May 2016 09:43:00 -0700 From: Guenter Roeck To: Timur Tabi Cc: Pratyush Anand , fu.wei@linaro.org, Suravee.Suthikulpanit@amd.com, wim@iguana.be, linux-arm-kernel@lists.infradead.org, linux-watchdog@vger.kernel.org, open list , Dave Young Subject: Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Message-ID: <20160505164300.GA16914@roeck-us.net> References: <20da73bb9bdf27993514c1da80fead13dc92932d.1462262900.git.panand@redhat.com> <5728A7C3.4010001@roeck-us.net> <20160503143856.GE13045@dhcppc6.redhat.com> <5728BEC4.6050603@codeaurora.org> <20160503155141.GF13045@dhcppc6.redhat.com> <20160503171602.GA2518@roeck-us.net> <20160504141449.GG13045@dhcppc6.redhat.com> <572A0577.1070000@codeaurora.org> <20160504155932.GH13045@dhcppc6.redhat.com> <572A2099.4070901@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <572A2099.4070901@codeaurora.org> User-Agent: Mutt/1.5.23 (2014-03-12) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: guenter@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 04, 2016 at 11:17:29AM -0500, Timur Tabi wrote: > Pratyush Anand wrote: > >Its unique to SBSA because you have very little timeout here. kexec-tools > >upstream does not have any mechanism to handle watchdog timeout. Lets say even > >if we implement a framework there, the best it can do is to ping the watchdog > >again. > > Ok, so it's more accurate to say that kexec has a minimum watchdog timeout > requirement. What happens if the system admin sets the timeout to 5 seconds > arbitrarily? The system will reset during kexec, no matter which hardware > is used. > > This still sounds like a band-aid to me. We're just assuming that we need a > timeout of at least 20 seconds to support kexec. Frankly, this still sounds > like a problem the kexec developers needs to acknowledge and deal with. > > Still I'm okay with a patch that extends the timeout by programming WCV, but > it has to be commented as a hack specifically to support kexec because the > timeout might be too short. Then Wim can decide whether he supports such > changes. > I don't even understand how kexec-tools is involved in the first place. kexec-tools sounds like user space, which should execute _after_ the kernel and its modules are loaded (assuming modules are loaded from initramfs). If kexec-tools can somehow ping the watchdog (presumably by writing into the HW directly), I don't understand why it doesn't simply load the watchdog driver instead and let the watchdog core handle the heartbeats. I am really missing something here. How can kexec-tools do anything before the kernel is loaded ? Guenter