Re: [PATCH v3 4/7] livepatch: Deprecate stack_order

[Petr Mladek <pmladek@suse.com>]

On Sun 2026-06-07 21:16:56, Yafang Shao wrote:
> stack_order is no longer needed for atomic-replace livepatches, as a
> single function can only be modified by a unique replace_set.
> To maintain backward compatibility, print a dummy value, as suggested by
> sashiko-bot.

I would personally remove it completely. I believe that there are
only few users around the world. And they will need to update
the tooling/strategy for the new "replace_set" anyway.

> --- /dev/null
> +++ b/Documentation/ABI/removed/sysfs-kernel-livepatch
> @@ -0,0 +1,9 @@
> +What:		/sys/kernel/livepatch/<patch>/stack_order
> +Date:		Jan 2025
> +KernelVersion:	6.14.0
> +Description:
> +		This attribute specifies the sequence in which live patch modules
> +		are applied to the system. If multiple live patches modify the same
> +		function, the implementation with the biggest 'stack_order' number
> +		is used, unless a transition is currently in progress.

I was not aware of this ABI/removed part. We should put here also
the livepatch/replace interface which was removed in the 3rd patch.

> --- a/tools/testing/selftests/livepatch/test-sysfs.sh
> +++ b/tools/testing/selftests/livepatch/test-sysfs.sh
> @@ -21,8 +21,6 @@ check_sysfs_rights "$MOD_LIVEPATCH" "enabled" "-rw-r--r--"
>  check_sysfs_value  "$MOD_LIVEPATCH" "enabled" "1"
>  check_sysfs_rights "$MOD_LIVEPATCH" "force" "--w-------"
>  check_sysfs_rights "$MOD_LIVEPATCH" "replace" "-r--r--r--"
> -check_sysfs_rights "$MOD_LIVEPATCH" "stack_order" "-r--r--r--"
> -check_sysfs_value  "$MOD_LIVEPATCH" "stack_order" "1"
>  check_sysfs_rights "$MOD_LIVEPATCH" "transition" "-r--r--r--"
>  check_sysfs_value  "$MOD_LIVEPATCH" "transition" "0"
>  check_sysfs_rights "$MOD_LIVEPATCH" "vmlinux/patched" "-r--r--r--"
> @@ -135,71 +133,4 @@ livepatch: '$MOD_LIVEPATCH': completing unpatching transition
>  livepatch: '$MOD_LIVEPATCH': unpatching complete
>  % rmmod $MOD_LIVEPATCH"
>  
> -start_test "sysfs test stack_order value"
> -

This is not longer needed in linux-next. Marcos made the test optional,
see
https://lore.kernel.org/all/20260504-lp-tests-old-fixes-v5-6-0be26d94ab9a@suse.com/

The changes are queued for 7.2 merge window which will likely start
next week.

I suggest to wait with v4 until the change is merged. We should wait
for opinion from others (Miroslav, Josh, Joe, Song) anyway. We
need to be sure that the change of the semantic is acceptable
in general.


> -load_lp $MOD_LIVEPATCH
> -
> -check_sysfs_value  "$MOD_LIVEPATCH" "stack_order" "1"
> -
> -load_lp $MOD_LIVEPATCH2
> -
> -check_sysfs_value  "$MOD_LIVEPATCH2" "stack_order" "2"
> -
> -load_lp $MOD_LIVEPATCH3

Nit: It seems that MOD_LIVEPATCH2 and MOD_LIVEPATCH3 are not longer used
     at least in this test-sysfs.sh file. Well, I guess that we will
     keep this test optional for older kernels.

> -check_sysfs_value  "$MOD_LIVEPATCH3" "stack_order" "3"
> -

Best Regards,
Petr