On 26.05.22 15:39, Sourabh Jain wrote: > Hello Eric, > > On 26/05/22 18:46, Eric DeVolder wrote: >> >> >> On 5/25/22 10:13, Sourabh Jain wrote: >>> Hello Eric, >>> >>> On 06/05/22 00:15, Eric DeVolder wrote: >>>> When the kdump service is loaded, if a CPU or memory is hot >>>> un/plugged, the crash elfcorehdr (for x86), 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 (e. 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. No involvement >>>> with userspace needed. >>>> >>>> To realize the benefits/test this patchset, one must make a couple >>>> of minor changes to userspace: >>>> >>>> - Disable the udev rule for updating kdump on hot un/plug changes. >>>> Add the following as the first two lines to the udev rule file >>>> /usr/lib/udev/rules.d/98-kexec.rules: >>> >>> If we can have a sysfs attribute to advertise this feature then >>> userspace >>> utilities (kexec tool/udev rules) can take action accordingly. In >>> short, it will >>> help us maintain backward compatibility. >>> >>> kexec tool can use the new sysfs attribute and allocate additional >>> buffer space >>> for elfcorehdr accordingly. Similarly, the checksum-related changes >>> can come >>> under this check. >>> >>> Udev rule can use this sysfs file to decide kdump service reload is >>> required or not. >> >> Great idea. I've been working on the corresponding udev and >> kexec-tools changes and your input/idea here is quite timely. >> >> I have boolean "crash_hotplug" as a core_param(), so it will show up as: >> >> # cat /sys/module/kernel/parameters/crash_hotplug >> N > > How about using 0-1 instead Y/N? > 0 = crash hotplug not supported > 1 = crash hotplug supported > > Also how about keeping sysfs here instead? > /sys/kernel/kexec_crash_hotplug It's not only about hotplug, though. And actually we care about onlining/offlining. Hmm, I wonder if there is a better name for this automatic handling of cpu and memory devices. -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
