Hello Thomas,
On 01/02/23 17:03, Thomas Gleixner wrote:
Eric!
On Tue, Jan 31 2023 at 17:42, Eric DeVolder wrote:
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,14 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
/* Prepare one phdr of type PT_NOTE for each present CPU */
for_each_present_cpu(cpu) {
+#ifdef CONFIG_CRASH_HOTPLUG
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
+ /* Skip the soon-to-be offlined cpu */
+ if ((image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU) &&
+ (cpu == image->offlinecpu))
+ continue;
+ }
+#endif
I'm failing to see how the above is correct in any way. Look at the
following sequence of events:
1) Offline CPU$N
-> Prepare elf headers with CPU$N excluded
2) Another hotplug operation != 'Online CPU$N'
-> Prepare elf headers with CPU$N included
Also in case of loading the crash kernel in the situation where not all
present CPUs are online (think boot time SMT disable) then your
resulting crash image will contain all present CPUs and none of the
offline CPUs are excluded.
How does that make any sense at all?
This image->hp_action and image->offlinecpu dance is engineering
voodoo. You just can do:
for_each_present_cpu(cpu) {
if (!cpu_online(cpu))
continue;
do_stuff(cpu);
which does the right thing in all situations and can be further
simplified to:
for_each_online_cpu(cpu) {
do_stuff(cpu);
What will be the implication on x86 if we pack PT_NOTE for possible CPUs?
IIUC, on boot the crash notes are create for possible CPUs using pcpu_alloc
and when the system is on crash path the crash notes for online CPUs is
populated with the required data and rest crash notes are untouched.
And I think the /proc/vmcore generation in kdump/second kernel and
makedumpfile do
take care of empty crash notes belong to offline CPUs.
Any thoughts?
Thanks,
Sourabh
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