On 02/02/24 at 10:53am, Hari Bathini wrote:

Hi Baoquan,

On 19/01/24 8:22 pm, Baoquan He wrote:

quoted

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/ (local)

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

quoted

                                                     ---->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
# end of Kexec and crash features

(2) set CONFIG_KEXEC_FILE and 'make olddefconfig':
---------------
# Kexec and crash features
CONFIG_CRASH_RESERVE=y
CONFIG_VMCORE_INFO=y
CONFIG_KEXEC_CORE=y
CONFIG_KEXEC_FILE=y
CONFIG_CRASH_DUMP=y
CONFIG_CRASH_HOTPLUG=y
CONFIG_CRASH_MAX_MEMORY_RANGES=8192
# end of Kexec and crash features
---------------

(3) unset CONFIG_CRASH_DUMP in case 2 and execute 'make olddefconfig':
------------------------
# Kexec and crash features
CONFIG_KEXEC_CORE=y
CONFIG_KEXEC_FILE=y
# end of Kexec and crash features
------------------------

Note:
For ppc, it needs investigation to make clear how to split out crash
code in arch folder.

On powerpc, both kdump and fadump need PROC_VMCORE & CRASH_DUMP.
Hope that clears things. So, patch 3/14 breaks things for FA_DUMP..

I see it now. We can easily fix that with below patch. What do you
think?

By the way, do you have chance to help test these on powerpc system?
I can find ppc64le machine, while I don't know how to operate to test
fadump.

From fa8e6c3930d4f22f2b3768399c5bf0523c17adde Mon Sep 17 00:00:00 2001
From: Baoquan He <redacted>
Date: Sun, 4 Feb 2024 11:06:54 +0800
Subject: [PATCH] power/fadump: make FA_DUMP select CRASH_DUMP
Content-type: text/plain

FA_DUMP which is similar with kdump needs vmcoreinfo exporting,
crashkernel reservation and /proc/vmcore file . After refactoring crash
related codes and Kconfig items, make FA_DUMP select CRASH_DUMP. Now
the dependency layout is like below:

                           ---->VMCORE_INFO
                         /|
FA_DUMP--> CRASH_DUMP-->/-|---->CRASH_RESERVE
                        \ |
                          \---->PROC_VMCORE

Signed-off-by: Baoquan He <redacted>
---
 arch/powerpc/Kconfig | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index f182fb354bef..d5d4c890f010 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -695,8 +695,7 @@ config ARCH_SELECTS_CRASH_DUMP
 config FA_DUMP
 	bool "Firmware-assisted dump"
 	depends on PPC64 && (PPC_RTAS || PPC_POWERNV)
-	select VMCORE_INFO
-	select CRASH_RESERVE
+	select CRASH_DUMP
 	help
 	  A robust mechanism to get reliable kernel crash dump with
 	  assistance from firmware. This approach does not use kexec,

-- 
2.41.0


> 
> > Hope Hari and Pingfan can help have a look, see if
> > it's doable. Now, I make it either have both kexec and crash enabled, or
> > disable both of them altogether.
> 
> 
> Sure. I will take a closer look...

Thanks a lot. Please feel free to post patches to make that, or I can do
it with your support or suggestion.