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Fri, 25 Mar 2022 08:32:47 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7D127AE051; Fri, 25 Mar 2022 08:32:45 +0000 (GMT) Received: from [9.43.55.110] (unknown [9.43.55.110]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 25 Mar 2022 08:32:45 +0000 (GMT) Message-ID: Date: Fri, 25 Mar 2022 14:02:44 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [RFC v3 PATCH 0/5] In kernel handling of CPU hotplug events for crash kernel Content-Language: en-US To: Eric DeVolder , linuxppc-dev@ozlabs.org, mpe@ellerman.id.au References: <20220321080422.56255-1-sourabhjain@linux.ibm.com> From: Sourabh Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-GUID: QkS16xZ8AjD_m2CtxvuF4IjKB0ExrXvG X-Proofpoint-ORIG-GUID: DgdOJbVX5p7Y_dsloPkju13uwTR4GAYj Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.850,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-03-25_02,2022-03-24_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 bulkscore=0 phishscore=0 clxscore=1015 malwarescore=0 impostorscore=0 priorityscore=1501 mlxscore=0 suspectscore=0 adultscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2203250046 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mahesh@linux.vnet.ibm.com, kexec@lists.infradead.org, bhe@redhat.com, hbathini@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 24/03/22 00:02, Eric DeVolder wrote: > > > On 3/21/22 03:04, Sourabh Jain wrote: >> This patch series implements the crash hotplug handler on PowerPC >> introduced >> by https://lkml.org/lkml/2022/3/3/674 patch series. >> >> >> The Problem: >> ============ >> Post hotplug/DLPAR events the capture kernel holds stale information >> about the >> system. Dump collection with stale capture kernel might end up in >> dump capture >> failure or an inaccurate dump collection. >> >> >> Existing solution: >> ================== >> The existing solution to keep the capture kernel up-to-date is >> observe the >> hotplug event via udev rule and trigger a full capture kernel reload >> post >> hotplug event. >> >> Shortcomings: >> ------------------------------------------------ >> - Leaves a window where kernel crash might not lead to successful dump >>    collection. >> - Reloading all kexec components for each hotplug is inefficient. >> Since only >>    one or two kexec components need to be updated due to hotplug >> event reloading >>    all kexec component is redundant. >> - udev rules are prone to races if hotplug events are frequent. >> >> More about issues with an existing solution is posted here: >>   - https://lkml.org/lkml/2020/12/14/532 >>   - >> https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-February/240254.html >> >> Proposed Solution: >> ================== >> Instead of reloading all kexec segments on hotplug event, this patch >> series >> focuses on updating only the relevant kexec segment. Once the kexec >> segments are loaded in the kernel reserved area then an arch-specific >> hotplug handler >> will update the relevant kexec segment based on hotplug event type. >> >> As mentioned above this patch series implemented a PowerPC crash hotplug >> handler for the CPU. The crash hotplug handler memory is in our TODO >> list. >> >> >> A couple of minor changes are required to realize the benefit of the >> patch >> series: >> >> - disalble the udev rule: >> >>    comment out the below line in kdump udev rule file: > fwiw, this will need to be conditionalized on arch, ie to skip for > ppc64. I'm doing the same for x86_64. I think kexec-tools maintains a separate udev rule file for PowerPC. I will ensure CPU rules gets removed from kdump udev rules once this feature is upstream. Thanks, - Sourabh Jain