From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 1/3] panic: Disable crash_kexec_post_notifiers if kdump is not available Date: Tue, 14 Jul 2015 13:01:12 -0500 Message-ID: <87si8qmxef.fsf@x220.int.ebiederm.org> References: <20150713202611.GA16525@fifo99.com> <87h9p7r0we.fsf@x220.int.ebiederm.org> <20150714135919.GA18333@fifo99.com> <20150714150208.GD10792@redhat.com> <20150714153430.GA18766@fifo99.com> <20150714154040.GA3912@redhat.com> <20150714154833.GA18883@fifo99.com> <20150714161612.GH10792@redhat.com> <87a8uyoeig.fsf@x220.int.ebiederm.org> <20150714172953.GA19135@fifo99.com> <20150714175527.GI10792@redhat.com> Mime-Version: 1.0 Return-path: In-Reply-To: <20150714175527.GI10792@redhat.com> (Vivek Goyal's message of "Tue, 14 Jul 2015 13:55:27 -0400") Sender: linux-sh-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Vivek Goyal Cc: dwalker@fifo99.com, Hidehiro Kawai , Andrew Morton , linux-mips@linux-mips.org, Baoquan He , linux-sh@vger.kernel.org, linux-s390@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Ingo Molnar , HATAYAMA Daisuke , Masami Hiramatsu , linuxppc-dev@lists.ozlabs.org, linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org Vivek Goyal writes: > On Tue, Jul 14, 2015 at 05:29:53PM +0000, dwalker@fifo99.com wrote: > > [..] >> > >> > If a machine is failing, there are high chance it can't deliver you the >> > >> > notification. Detecting that failure suing some kind of polling mechanism >> > >> > might be more reliable. And it will make even kdump mechanism more >> > >> > reliable so that it does not have to run panic notifiers after the crash. >> > >> >> > >> I think what your suggesting is that my company should change how it's hardware works >> > >> and that's not really an option for me. This isn't a simple thing like checking over the >> > >> network if the machine is down or not, this is way more complex hardware design. >> > > >> > > That means you are ready to live with an unreliable design. There might be >> > > cases where notifier does not get run properly and you will not do switch >> > > despite the fact that OS has failed. I was just trying to nudge you in >> > > a direction which could be more reliable mechanism. >> > >> > Sigh I see some deep confusion going on here. >> > >> > The panic notifiers are just that panic notifiers. They have not been >> > nor should they be tied to kexec. If those notifiers force a switch >> > over of between machines I fail to see why you would care if it was >> > kexec or another panic situation that is forcing that switchover. >> >> Hidehiro isn't fixing the failover situation on my side, he's fixing register >> information collection when crash_kexec_post_notifiers is used. > > Sure. Given that we have created this new parameter, let us fix it so that > we can capture the other cpu register state in crash dump. > > I am little disappointed that it was not tested well when this parameter was > introuced. We should have atleast tested it to the extent to see if there > is proper cpu state present for all cpus in the crash dump. > > At that point of time it looked like a simple modification > to allow panic notifiers before crash_kexec(). Either that or we say no one cares enough, and it known broken so let's just revert the fool thing. I honestly can't see how to support panic notifiers, before kexec. There is no way to tell what is being done and all of the pieces including smp_send_stop are known to be buggy. It isn't like this latest set of patches was reviewed/tested much better, as the first patch was wrong. Eric