Re: Crash on boot with CONFIG_JUMP_LABEL in 6.10

[matoro <matoro_mailinglist_kernel@matoro.tk>]

On 2024-07-30 09:50, John David Anglin wrote:
> On 2024-07-30 9:41 a.m., John David Anglin wrote:
>> On 2024-07-29 7:11 p.m., matoro wrote:
>>> Hi all, just bumped to the newest mainline starting with 6.10.2 and 
>>> immediately ran into a crash on boot. Fully reproducible, reverting back 
>>> to last known good (6.9.8) resolves the issue.  Any clue what's going on 
>>> here? I can provide full boot logs, start bisecting, etc if needed...
>> 6.10.2 built and booted okay on my c8000 with the attached config. You 
>> could start
>> with it and incrementally add features to try to identify the one that 
>> causes boot failure.
> Oh, I have an experimental clocksource patch installed.  You will need to 
> regenerate config
> with "make oldconfig" to use the current timer code.  Probably, this would 
> happen automatically.
>> 
>> Your config would be needed to duplicate.    Full boot log would also help.
> 
> Dave

Hi Dave, bisecting quickly revealed the cause here.

91a1d97ef482c1e4c9d4c1c656a53b0f6b16d0ed is the first bad commit
commit 91a1d97ef482c1e4c9d4c1c656a53b0f6b16d0ed
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Wed Mar 13 19:01:03 2024 +0100

     jump_label,module: Don't alloc static_key_mod for __ro_after_init keys

     When a static_key is marked ro_after_init, its state will never change
     (after init), therefore jump_label_update() will never need to iterate
     the entries, and thus module load won't actually need to track this --
     avoiding the static_key::next write.

     Therefore, mark these keys such that jump_label_add_module() might
     recognise them and avoid the modification.

     Use the special state: 'static_key_linked(key) && !static_key_mod(key)'
     to denote such keys.

     jump_label_add_module() does not exist under CONFIG_JUMP_LABEL=n, so the
     newly-introduced jump_label_init_ro() can be defined as a nop for that
     configuration.

     [ mingo: Renamed jump_label_ro() to jump_label_init_ro() ]

     Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
     Signed-off-by: Valentin Schneider <vschneid@redhat.com>
     Signed-off-by: Ingo Molnar <mingo@kernel.org>
     Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
     Link: 
https://lore.kernel.org/r/20240313180106.2917308-2-vschneid@redhat.com

  include/asm-generic/sections.h |  5 ++++
  include/linux/jump_label.h     |  3 +++
  init/main.c                    |  1 +
  kernel/jump_label.c            | 53 
++++++++++++++++++++++++++++++++++++++++++
  4 files changed, 62 insertions(+)

This only manifests with CONFIG_JUMP_LABEL=y, which I have set and you do 
not.  Flipping this off allows 6.10 to boot normally.  Copying in the author 
here as well.