Messages in this thread | | | Date | Mon, 1 May 2023 13:35:03 -0500 | Subject | Re: [PATCH v21 0/7] crash: Kernel handling of CPU and memory hot un/plug | From | Eric DeVolder <> |
| |
On 4/27/23 02:08, Hari Bathini wrote: > Hi Eric, > > On 04/04/23 11:33 pm, Eric DeVolder wrote: >> Once the kdump service is loaded, if changes to CPUs or memory occur, >> either by hot un/plug or off/onlining, the crash elfcorehdr must also >> be updated. >> >> The elfcorehdr describes to kdump the CPUs and memory in the system, >> and any inaccuracies can result in a vmcore with missing 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, purgatory and >> elfcorehdr) by the userspace kexec utility. In the original post I >> outlined the significant performance problems related to offloading >> this activity to userspace. >> >> This patchset introduces a generic crash handler that registers with >> the CPU and memory notifiers. Upon CPU or memory changes, from either >> hot un/plug or off/onlining, 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 elfcorehdr update. >> >> Note the description in patch 'crash: change crash_prepare_elf64_headers() >> to for_each_possible_cpu()' and 'x86/crash: optimize CPU changes' that >> enables further optimizations related to CPU plug/unplug/online/offline >> performance of elfcorehdr 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 updates the 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" >> >> With this changeset applied, the two rules evaluate to false for >> CPU and memory change events and thus skip the userspace >> unload-then-reload of kdump. >> >> - 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 > > With the in-kernel update, the size is anyway getting calculated in > kernel for kexec_file_load case, how about passing the recommended size > for elfcorehdr segment and any other segment that needs an in-kernel update as a sysfs attribute > instead of kexec-tools having to do the > calculation again in the userspace (get_elfcorehdrsz()) for kexec_load > case. That makes segment size calculation less error prone. > > Thanks > Hari Makes sense, I'll add that to v22. Thanks! eric
| |