[PATCH v10 0/5] PowerPC: In-kernel handling of CPU/Memory hotplug/online/offline events for kdump kernel
Eric DeVolder
eric.devolder at oracle.com
Tue Apr 25 00:05:19 AEST 2023
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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