From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sourabh Jain Date: Fri, 25 Mar 2022 14:02:44 +0530 Subject: [RFC v3 PATCH 0/5] In kernel handling of CPU hotplug events for crash kernel In-Reply-To: References: <20220321080422.56255-1-sourabhjain@linux.ibm.com> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org 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