Re: [PATCH v5 4/8] crash: generic crash hotplug support infrastructure

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On 15/03/22 19:42, Eric DeVolder wrote:


On 3/15/22 07:08, Sourabh Jain wrote:
Hello Eric,

On 03/03/22 21:57, Eric DeVolder wrote:
This patch introduces a generic crash hot plug/unplug infrastructure
for CPU and memory changes. Upon CPU and memory changes, a generic
crash_hotplug_handler() obtains the appropriate lock, does some
important house keeping and then dispatches the hot plug/unplug event
to the architecture specific arch_crash_hotplug_handler(), and when
that handler returns, the lock is released.

This patch modifies crash_core.c to implement a subsys_initcall()
function that installs handlers for hot plug/unplug events. If CPU
hotplug is enabled, then cpuhp_setup_state() is invoked to register a
handler for CPU changes. Similarly, if memory hotplug is enabled, then
register_memory_notifier() is invoked to install a handler for memory
changes. These handlers in turn invoke the common generic handler
crash_hotplug_handler().

On the CPU side, cpuhp_setup_state_nocalls() is invoked with parameter
CPUHP_AP_ONLINE_DYN. While this works, when a CPU is being unplugged,
the CPU still shows up in foreach_present_cpu() during the regeneration
of the new CPU list, thus the need to explicitly check and exclude the
soon-to-be offlined CPU in crash_prepare_elf64_headers().

On the memory side, each un/plugged memory block passes through the
handler. For example, if a 1GiB DIMM is hotplugged, that generate 8
memory events, one for each 128MiB memblock.

Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
---
  include/linux/kexec.h |  16 +++++++
  kernel/crash_core.c   | 108 ++++++++++++++++++++++++++++++++++++++++++
  2 files changed, 124 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index d7b59248441b..b11d75a6b2bc 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -300,6 +300,13 @@ struct kimage {
      /* Information for loading purgatory */
      struct purgatory_info purgatory_info;
+
+#ifdef CONFIG_CRASH_HOTPLUG
+    bool hotplug_event;
+    int offlinecpu;
+    bool elf_index_valid;
+    int elf_index;

How about keeping an array to track all kexec segment index need to be updated in
crash hotplug handler.

struct hp_segment {
    name;
    index;
    is_valid;
  }

It will be helpful if architecture need to updated multiple kexec segments  for a hotplug event.

For example, on PowerPC, we might need to update FDT and elfcorehdr on memory hot plug/unplug.

Thanks,
Sourabh Jain

Sourabh,
I'm OK with that. Another idea might be if there are just two, and one of them is elfcorehdr, then perhaps in addition to elf_index and elf_index_valid, maybe we add an arch_index and arch_index_valid? In the case of PPC, the FDT would be stored in arch_index?

Yes it seems like we might not need to keep more than two kexec indexes. Since this indexes are arch specific lets push them to struct kimage_arch (part of kimage). So for now I will push fdt_index to struct kimage_arch.

Thanks,
Sourabh Jain


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