On 5/26/22 08:39, 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
Yes, that makes more sense.
Thanks!
eric
Thanks,
Souabh Jain
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