From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by lists.ozlabs.org (Postfix) with ESMTP id BFE451A0834 for ; Wed, 4 Jun 2014 23:47:26 +1000 (EST) Date: Wed, 4 Jun 2014 09:46:49 -0400 From: Vivek Goyal To: "Srivatsa S. Bhat" Subject: Re: [PATCH] powerpc, kexec: Fix "Processor X is stuck" issue during kexec from ST mode Message-ID: <20140604134649.GB27557@redhat.com> References: <20140527105511.24309.74320.stgit@srivatsabhat.in.ibm.com> <20140528133143.GK14863@redhat.com> <538E2FF8.8060707@linux.vnet.ibm.com> <1401833365.3247.36.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1401833365.3247.36.camel@pasglop> Cc: ego@linux.vnet.ibm.com, matt@ozlabs.org, mahesh@linux.vnet.ibm.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, suzuki@in.ibm.com, ebiederm@xmission.com, paulus@samba.org, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jun 04, 2014 at 08:09:25AM +1000, Benjamin Herrenschmidt wrote: > On Wed, 2014-06-04 at 01:58 +0530, Srivatsa S. Bhat wrote: > > Yep, that makes sense. But unfortunately I don't have enough insight into > > why exactly powerpc has to online the CPUs before doing a kexec. I just > > know from the commit log and the comment mentioned above (and from my own > > experiments) that the CPUs will get stuck if they were offline. Perhaps > > somebody more knowledgeable can explain this in detail and suggest a proper > > long-term solution. > > > > Matt, Ben, any thoughts on this? > > The problem is with our "soft offline" which we do on some platforms. When we > offline we don't actually send the CPUs back to firmware or anything like that. > > We put them into a very low low power loop inside Linux. > > The new kernel has no way to extract them from that loop. So we must re-"online" > them before we kexec so they can be passed to the new kernel normally (or returned > to firmware like we do on powernv). Srivatsa, Looks like your patch has been merged. I don't like the following change in arch independent code. /* * migrate_to_reboot_cpu() disables CPU hotplug assuming that * no further code needs to use CPU hotplug (which is true in * the reboot case). However, the kexec path depends on using * CPU hotplug again; so re-enable it here. */ cpu_hotplug_enable(); As it is very powerpc specific requirement, can you enable hotplug in powerpc arch dependent code as a short term solution. Ideally one needs to fix the requirement of online all cpus in powerpc as a long term solution and then get rid of hotplug enable call. Thanks Vivek