Re: [PATCH 10/11] mm/zsmalloc: Handle single object charge migration in migrate_zspage

[Joshua Hahn]

On Thu, 12 Mar 2026 11:51:59 +0800 kernel test robot <lkp@xxxxxxxxx> wrote:

> Hi Joshua,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on axboe/for-next]
> [also build test WARNING on linus/master v7.0-rc3]
> [cannot apply to akpm-mm/mm-everything next-20260311]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Joshua-Hahn/mm-zsmalloc-Rename-zs_object_copy-to-zs_obj_copy/20260312-035531
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
> patch link:    https://lore.kernel.org/r/20260311195153.4013476-11-joshua.hahnjy%40gmail.com
> patch subject: [PATCH 10/11] mm/zsmalloc: Handle single object charge migration in migrate_zspage
> config: x86_64-randconfig-001-20260312 (https://download.01.org/0day-ci/archive/20260312/202603121158.g93vlc2U-lkp@xxxxxxxxx/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260312/202603121158.g93vlc2U-lkp@xxxxxxxxx/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202603121158.g93vlc2U-lkp@xxxxxxxxx/
> 
> All warnings (new ones prefixed by >>):
> 
> >> mm/zsmalloc.c:1702:6: warning: variable 's_idx' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>     1702 |         if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
>          |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    mm/zsmalloc.c:1752:45: note: uninitialized use occurs here
>     1752 |         d_zspage->objcgs[d_idx] = s_zspage->objcgs[s_idx];
>          |                                                    ^~~~~
>    mm/zsmalloc.c:1702:2: note: remove the 'if' if its condition is always false
>     1702 |         if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
>          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     1703 |                 goto out;
>          |                 ~~~~~~~~
>    mm/zsmalloc.c:1696:20: note: initialize the variable 's_idx' to silence this warning
>     1696 |         unsigned int s_idx, d_idx;
>          |                           ^
>          |                            = 0
> >> mm/zsmalloc.c:1702:6: warning: variable 'd_idx' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>     1702 |         if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
>          |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    mm/zsmalloc.c:1752:19: note: uninitialized use occurs here
>     1752 |         d_zspage->objcgs[d_idx] = s_zspage->objcgs[s_idx];
>          |                          ^~~~~
>    mm/zsmalloc.c:1702:2: note: remove the 'if' if its condition is always false
>     1702 |         if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
>          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     1703 |                 goto out;
>          |                 ~~~~~~~~
>    mm/zsmalloc.c:1696:27: note: initialize the variable 'd_idx' to silence this warning
>     1696 |         unsigned int s_idx, d_idx;
>          |                                  ^
>          |                                   = 0
>    2 warnings generated.

Hello kernel test robot,

Thank you for catching this issue! Yes, the MEMCG v1 check should be
done after I use obj_to_location to initialize the indices, so that
the objcg pointer swap works at the end.

Will make the change in the next version!
Joshua