Messages in this thread | | | Date | Wed, 23 Nov 2022 21:01:59 +0530 | Subject | Re: [PATCH v14 0/7] crash: Kernel handling of CPU and memory hot un/plug | From | Sourabh Jain <> |
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On 17/11/22 03:16, Eric DeVolder wrote: > When the kdump service is loaded, if a CPU or memory is hot > un/plugged, the crash elfcorehdr, which describes the CPUs > and memory in the system, must also be updated, else the resulting > vmcore is inaccurate (eg. missing either CPU context or memory > regions). > > The current solution utilizes udev to initiate an unload-then-reload > of the kdump image (eg. kernel, initrd, boot_params, puratory and > elfcorehdr) by the userspace kexec utility. In previous posts I have > outlined the significant performance problems related to offloading > this activity to userspace. > > This patchset introduces a generic crash hot un/plug handler that > registers with the CPU and memory notifiers. Upon CPU or memory > changes, this generic handler is invoked and performs important > housekeeping, for example obtaining the appropriate lock, and then > invokes an architecture specific handler to do the appropriate > updates. > > In the case of x86_64, the arch specific handler generates a new > elfcorehdr, and overwrites the old one in memory; thus no > involvement with userspace needed. > > To realize the benefits/test this patchset, one must make a couple > of minor changes to userspace: > > - Prevent udev from updating kdump crash kernel on hot un/plug changes. > Add the following as the first lines to the RHEL udev rule file > /usr/lib/udev/rules.d/98-kexec.rules: > > # The kernel handles updates to crash elfcorehdr for cpu and memory changes > SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" > SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" > > These lines will cause cpu and memory hot un/plug events to be > skipped within this rule file, with this changset applied. > > - Change to the kexec_file_load for loading the kdump kernel: > Eg. on RHEL: in /usr/bin/kdumpctl, change to: > standard_kexec_args="-p -d -s" > which adds the -s to select kexec_file_load syscall. > > This kernel patchset also supports kexec_load() with a modified kexec > userspace utility. A working changeset to the kexec userspace utility > is posted to the kexec-tools mailing list here: > > http://lists.infradead.org/pipermail/kexec/2022-October/026032.html > > To use the kexec-tools patch, apply, build and install kexec-tools, > then change the kdumpctl's standard_kexec_args to replace the -s with > --hotplug. The removal of -s reverts to the kexec_load syscall and > the addition of --hotplug invokes the changes put forth in the > kexec-tools patch. > > Regards, > eric > --- > v14: 16nov2022 > - Rebased onto 6.1.0-rc5 > - Introduced CRASH_HOTPLUG Kconfig item to better fine tune > compilation of feature components, per Boris. > - Removed hp_action parameter to arch_crash_handle_hotplug_event() > as it is unused.
But what if an architecture has different actions based on hp type?
- Sourabh Jain
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