[PATCH 0/5] crash: clean up kdump related config items

Baoquan He
2024-01-05T10:33:35Z

Motivation:
=============
Previously, LKP reported a building error. When investigating, it can't
be resolved reasonablly with the present messy kdump config items.

https://lore.kernel.org/oe-kbuild-all/202312182200.Ka7MzifQ-lkp@intel.com/

The kdump (crash dumping) related config items could causes confusions:

Firstly,
---
CRASH_CORE enables codes including
- crashkernel reservation parsing;
- elfcorehdr updating;
- vmcoreinfo saving;
- crash hotplug handling;

Now fadump of powerpc, kcore dynamic debugging and kdump all selects
CRASH_CORE, while fadump
- fadump needs crashkernel parsing, vmcoreinfo and accessing
global variable 'elfcorehdr_addr';
- kcore needs saved vmcoreinfo;
- kdump needs all of the current kernel/crash_core.c.

So only enabling PROC_CORE or FA_DUMP will enable CRASH_CORE will
confuse people that we enable the core code of kdump. Actually it's not.

Secondly,
---
It's not reasonable to allow KEXEC_CORE select CRASH_CORE.

Because KEXEC_CORE enables codes which allocate control pages, copy
kexec/kdump segments, and prepare for switching. These codes are
shared by both kexec_load and kexec_file_load, and by both kexec reboot
and kdump. We could want kexec reboot, but disable kdump. In that case,
CRASH_CORE should not be selected.

Thirdly,
---
It's not reasonable to allow CRASH_DUMP select KEXEC_CORE.

That could make KEXEC_CORE, CRASH_DUMP are enabled independently from
KEXEC or KEXEC_FILE. However, w/o KEXEC or KEXEC_FILE, the KEXEC_CORE
code built in doesn't make any sense because no kernel loading or
switching will happen to utilize the KEXEC_CORE code.

Changes:
===========
1, split CRASH_CORE codes into three parts:
1. move the elfcorehdr upating code and crash hotplug handling code
into kernel/kexec_core.c. Both KEXEC and KEXEC_FILE will use them.
2. split crashkernel reservation code out into kernel/crash_reserve.c,
add CRASH_RESERVE to control its enabling;
3. rename the left kernel/crash_core.c to kernel/vmcore_info.c since
only vmcoreinfo is saved in the file, and add VMCORE_INFO to
control its enabling;
2, rename the current kernel/crash_dump.c to kernel/elfcorehdr.c because
it only defines elfcorehdr_addr and function parse_elfcorehdr() in the
file. And build it in when VMCORE_INFO is enabled.

Achievement:
===========
With above changes, I can rearrange the config items as below (the right
item depends on or is selected by the left item):

PROC_KCORE -----------> VMCORE_INFO

|----------> VMCORE_INFO
FA_DUMP----|
|----------> CRASH_RESERVE

---->VMCORE_INFO
/
|---->CRASH_RESERVE
KEXEC --| /|
|--> KEXEC_CORE--> CRASH_DUMP-->/-|---->PROC_VMCORE
KEXEC_FILE --| \ |
\---->CRASH_HOTPLUG

KEXEC --|
|--> KEXEC_CORE (for kexec reboot only)
KEXEC_FILE --|

Baoquan He (5):
kexec_core: move kdump related codes from crash_core.c to kexec_core.c
kexec: split crashkernel reservation code out from crash_core.c
crash: rename crash_core to vmcore_info
crash: remove dependency of FA_DUMP on CRASH_DUMP
crash: clean up CRASH_DUMP

arch/arm64/Kconfig | 2 +-
.../asm/{crash_core.h => crash_reserve.h} | 4 +-
arch/arm64/kernel/Makefile | 2 +-
.../kernel/{crash_core.c => vmcore_info.c} | 2 +-
arch/powerpc/Kconfig | 4 +-
arch/powerpc/kernel/setup-common.c | 2 +-
arch/powerpc/mm/nohash/kaslr_booke.c | 4 +-
arch/powerpc/platforms/powernv/opal-core.c | 2 +-
arch/riscv/Kconfig | 2 +-
.../asm/{crash_core.h => crash_reserve.h} | 4 +-
arch/riscv/kernel/Makefile | 2 +-
.../kernel/{crash_core.c => vmcore_info.c} | 2 +-
arch/x86/Kconfig | 2 +-
.../asm/{crash_core.h => crash_reserve.h} | 6 +-
arch/x86/kernel/Makefile | 2 +-
.../{crash_core_32.c => vmcore_info_32.c} | 2 +-
.../{crash_core_64.c => vmcore_info_64.c} | 2 +-
drivers/firmware/qemu_fw_cfg.c | 14 +-
fs/proc/Kconfig | 2 +-
fs/proc/kcore.c | 2 +-
include/linux/buildid.h | 2 +-
include/linux/crash_reserve.h | 48 +
include/linux/kexec.h | 27 +-
include/linux/{crash_core.h => vmcore_info.h} | 78 +-
kernel/Kconfig.kexec | 12 +-
kernel/Makefile | 4 +-
kernel/crash_core.c | 1065 -----------------
kernel/crash_reserve.c | 453 +++++++
kernel/{crash_dump.c => elfcorehdr.c} | 0
kernel/kexec_core.c | 408 +++++++
kernel/kexec_internal.h | 2 +
kernel/ksysfs.c | 6 +-
kernel/printk/printk.c | 4 +-
kernel/vmcore_info.c | 233 ++++
lib/buildid.c | 2 +-
35 files changed, 1222 insertions(+), 1186 deletions(-)
rename arch/arm64/include/asm/{crash_core.h => crash_reserve.h} (81%)
rename arch/arm64/kernel/{crash_core.c => vmcore_info.c} (97%)
rename arch/riscv/include/asm/{crash_core.h => crash_reserve.h} (78%)
rename arch/riscv/kernel/{crash_core.c => vmcore_info.c} (96%)
rename arch/x86/include/asm/{crash_core.h => crash_reserve.h} (92%)
rename arch/x86/kernel/{crash_core_32.c => vmcore_info_32.c} (90%)
rename arch/x86/kernel/{crash_core_64.c => vmcore_info_64.c} (94%)
create mode 100644 include/linux/crash_reserve.h
rename include/linux/{crash_core.h => vmcore_info.h} (59%)
delete mode 100644 kernel/crash_core.c
create mode 100644 kernel/crash_reserve.c
rename kernel/{crash_dump.c => elfcorehdr.c} (100%)
create mode 100644 kernel/vmcore_info.c