On 4/23/23 05:52, Sourabh Jain wrote:
The Problem:
============
Post CPU/Memory hot plug/unplug and online/offline events the kernel
holds stale information about the system. Dump collection with stale
kdump kernel might end up in dump capture failure or an inaccurate dump
collection.
Existing solution:
==================
The existing solution to keep the kdump kernel up-to-date by monitoring
CPU/Memory hotplug/online/offline events via udev rule and trigger a full
kdump kernel reload for every hotplug event.
Shortcomings:
------------------------------------------------
- Leaves a window where kernel crash might not lead to a successful dump
collection.
- Reloading all kexec components for each hotplug is inefficient.
- udev rules are prone to races if hotplug events are frequent.
More about issues with an existing solution is posted here:
- https://lkml.org/lkml/2020/12/14/532
- https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-February/240254.html
Proposed Solution:
==================
Instead of reloading all kexec segments on CPU/Memory hotplug/online/offline
event, this patch series focuses on updating only the relevant kexec segment.
Once the kexec segments are loaded in the kernel reserved area then an
arch-specific hotplug handler will update the relevant kexec segment based on
hotplug event type.
Series Dependencies
====================
This patch series implements the crash hotplug handler on PowerPC. The generic
crash hotplug handler is introduced by https://lkml.org/lkml/2023/4/4/1136 patch
series.
Git tree for testing:
=====================
The below git tree has this patch series applied on top of dependent patch
series.
https://github.com/sourabhjains/linux/tree/e21-s10
To realise the feature the kdump udev rule must updated to avoid
reloading of kdump reload on CPU/Memory hotplug/online/offline events.
RHEL: /usr/lib/udev/rules.d/98-kexec.rules
-SUBSYSTEM=="cpu", ACTION=="online", GOTO="kdump_reload_cpu"
-SUBSYSTEM=="memory", ACTION=="online", GOTO="kdump_reload_mem"
-SUBSYSTEM=="memory", ACTION=="offline", GOTO="kdump_reload_mem"
+SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
+SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
I didn't see in the patch series where you would have the equivalent to the following (needed for
the sysfs crash_hotplug entries):
#ifdef CONFIG_HOTPLUG_CPU
static inline int crash_hotplug_cpu_support(void) { return 1; }
#define crash_hotplug_cpu_support crash_hotplug_cpu_support
#endif
#ifdef CONFIG_MEMORY_HOTPLUG
static inline int crash_hotplug_memory_support(void) { return 1; }
#define crash_hotplug_memory_support crash_hotplug_memory_support
#endif
Note: only kexec_file_load syscall will work. For kexec_load minor changes are
required in kexec tool.
---
Changelog:
v10:
- Drop the patch that adds fdt_index attribute to struct kimage_arch
Find the fdt segment index when needed.
- Added more details into commits messages.
- Rebased onto 6.3.0-rc5
v9:
- Removed patch to prepare elfcorehdr crash notes for possible CPUs.
The patch is moved to generic patch series that introduces generic
infrastructure for in kernel crash update.
- Removed patch to pass the hotplug action type to the arch crash
hotplug handler function. The generic patch series has introduced
the hotplug action type in kimage struct.
- Add detail commit message for better understanding.
v8:
- Restrict fdt_index initialization to machine_kexec_post_load
it work for both kexec_load and kexec_file_load.[3/8] Laurent Dufour
- Updated the logic to find the number of offline core. [6/8]
- Changed the logic to find the elfcore program header to accommodate
future memory ranges due memory hotplug events. [8/8]
v7
- added a new config to configure this feature
- pass hotplug action type to arch specific handler
v6
- Added crash memory hotplug support
v5:
- Replace COFNIG_CRASH_HOTPLUG with CONFIG_HOTPLUG_CPU.
- Move fdt segment identification for kexec_load case to load path
instead of crash hotplug handler
- Keep new attribute defined under kimage_arch to track FDT segment
under CONFIG_HOTPLUG_CPU config.
v4:
- Update the logic to find the additional space needed for hotadd CPUs post
kexec load. Refer "[RFC v4 PATCH 4/5] powerpc/crash hp: add crash hotplug
support for kexec_file_load" patch to know more about the change.
- Fix a couple of typo.
- Replace pr_err to pr_info_once to warn user about memory hotplug
support.
- In crash hotplug handle exit the for loop if FDT segment is found.
v3
- Move fdt_index and fdt_index_vaild variables to kimage_arch struct.
- Rebase patche on top of https://lkml.org/lkml/2022/3/3/674 [v5]
- Fixed warning reported by checpatch script
v2:
- Use generic hotplug handler introduced by https://lkml.org/lkml/2022/2/9/1406, a
significant change from v1.
Sourabh Jain (5):
powerpc/kexec: turn some static helper functions public
powerpc/crash: introduce a new config option CRASH_HOTPLUG
powerpc/crash: add crash CPU hotplug support
crash: forward memory_notify args to arch crash hotplug handler
powerpc/kexec: add crash memory hotplug support
arch/powerpc/Kconfig | 12 +
arch/powerpc/include/asm/kexec.h | 10 +
arch/powerpc/include/asm/kexec_ranges.h | 1 +
arch/powerpc/kexec/core_64.c | 301 ++++++++++++++++++++++++
arch/powerpc/kexec/elf_64.c | 12 +-
arch/powerpc/kexec/file_load_64.c | 212 ++++-------------
arch/powerpc/kexec/ranges.c | 85 +++++++
arch/x86/include/asm/kexec.h | 2 +-
arch/x86/kernel/crash.c | 3 +-
include/linux/kexec.h | 2 +-
kernel/crash_core.c | 14 +-
11 files changed, 479 insertions(+), 175 deletions(-)
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