On 02/02/24 at 10:53am, Hari Bathini wrote:
> Hi Baoquan,
>
> On 19/01/24 8:22 pm, Baoquan He wrote:
> > 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-...@intel.com/
> >
> > The kdump (crash dumping) related config items could causes confusions:
> >
> > Firstly,
> > ---
> > CRASH_CORE enables codes including
> > - crashkernel reservation;
> > - elfcorehdr updating;
> > - vmcoreinfo exporting;
> > - crash hotplug handling;
> >
> > Now fadump of powerpc, kcore dynamic debugging and kdump all selects
> > CRASH_CORE, while fadump
> > - fadump needs crashkernel parsing, vmcoreinfo exporting, and accessing
> > global variable 'elfcorehdr_addr';
> > - kcore only needs vmcoreinfo exporting;
> > - kdump needs all of the current kernel/crash_core.c.
> >
> > So only enabling PROC_CORE or FA_DUMP will enable CRASH_CORE, this
> > mislead people that we enable crash dumping, actual 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 reboot and kdump. We could want kexec reboot,
> > but disable kdump. In that case, CRASH_CORE should not be selected.
> >
> >
> > CONFIG_CRASH_CORE=y
> > CONFIG_KEXEC_CORE=y
> > CONFIG_KEXEC=y
> > CONFIG_KEXEC_FILE=y
> > -
> >
> > 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.
> > -
> > CONFIG_CRASH_CORE=y
> > CONFIG_KEXEC_CORE=y
> > CONFIG_CRASH_DUMP=y
> > -
> >
> > In this case, what is worse, on arch sh and arm, KEXEC relies on MMU,
> > while CRASH_DUMP can still be enabled when !MMU, then compiling error is
> > seen as the lkp test robot reported in above link.
> >
> > --arch/sh/Kconfig--
> > config ARCH_SUPPORTS_KEXEC
> > def_bool MMU
> >
> > config ARCH_SUPPORTS_CRASH_DUMP
> > def_bool BROKEN_ON_SMP
> > ---
> >
> > Changes:
> > ===
> > 1, split out crash_reserve.c from crash_core.c;
> > 2, split out vmcore_infoc. from crash_core.c;
> > 3, move crash related codes in kexec_core.c into crash_core.c;
> > 4, remove dependency of FA_DUMP on CRASH_DUMP;
> > 5, clean up kdump related config items;
> > 6, wrap up crash codes in crash related ifdefs on all 9 arch-es
> > which support crash dumping;
> >
> > Achievement:
> > ===
> > With above changes, I can rearrange the config item logic as below (the
> > right
> > item depends on or is selected by the left item):
> >
> > PROC_KCORE ---> VMCORE_INFO
> >
> > |--> VMCORE_INFO
> > FA_DUMP|
> > |--> CRASH_RESERVE
>
> FA_DUMP also needs PROC_VMCORE (CRASH_DUMP by dependency, I guess).
> So, the FA_DUMP related changes here will need a relook..
Thanks for checking this.
So FA_DUMP needs vmcoreinfo exporting, crashkernel reservation,
/proc/vmcore. Then it's easy to adjust the kernel config item of FA_DUMP
to make it select CRASH_DUMP. Except of this, do you have concern about
the current code and Kconfig refactorying?
>VMCORE_INFO
/|
FA_DUMP--> CRASH_DUMP-->/-|>CRASH_RESERVE
\ |
\>PROC_VMCORE
>
>
> > >VMCORE_INFO
> > /
> > |>CRASH_RESERVE
> > KEXEC --|/|
> > |--> KEXEC_CORE--> CRASH_DUMP-->/-|>PROC_VMCORE
> > KEXEC_FILE --| \ |
> > \>CRASH_HOTPLUG
> >
> >
> > KEXEC --|
> > |--> KEXEC_CORE (for kexec reboot only)
> > KEXEC_FILE --|
> >
> > Test
> >
> > On all 8 architectures, including x86_64, arm64, s390x, sh, arm, mips,
> > riscv, loongarch, I did below three cases of config item setting and
> > building all passed. Let me take configs on x86_64 as exampmle here:
> >
> > (1) Both CONFIG_KEXEC and KEXEC_FILE is unset, then all kexec/kdump
> > items are unset automatically:
> > # Kexec and crash features
> > # CONFIG_KEXEC is not set
> > # CONFIG_KEXEC_FILE is not set
