Subject: Re: linux-next: manual merge of the bpf-next tree with the mm-unstable tree

From: Roman Gushchin <[email-masked]>
Date: Mon, 05 Jan 2026 20:23:36 -0800

Alexei Starovoitov <[email-masked]> writes:

> On Sun, Jan 4, 2026 at 6:04 PM Stephen Rothwell <[email-masked]> wrote:
>>
>> Hi all,
>>
>> Today's linux-next merge of the bpf-next tree got a semantic conflict in:
>>
>>   include/linux/memcontrol.h
>>   mm/memcontrol-v1.c
>>   mm/memcontrol.c
>>
>> between commit:
>>
>>   eb557e10dcac ("memcg: move mem_cgroup_usage memcontrol-v1.c")
>>
>> from the mm-unstable tree and commit:
>>
>>   99430ab8b804 ("mm: introduce BPF kfuncs to access memcg statistics and events")
>>
>> from the bpf-next tree producing this build failure:
>>
>> mm/memcontrol-v1.c:430:22: error: static declaration of 'mem_cgroup_usage' follows non-static declaration
>>   430 | static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
>>       |                      ^~~~~~~~~~~~~~~~
>> In file included from mm/memcontrol-v1.c:3:
>> include/linux/memcontrol.h:953:15: note: previous declaration of
>> 'mem_cgroup_usage' with type 'long unsigned int(struct mem_cgroup *,
>> bool)' {aka 'long unsigned int(struct mem_cgroup *, _Bool)'}
>>   953 | unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
>>       |               ^~~~~~~~~~~~~~~~
>>
>> I fixed it up (I reverted the mm-unstable tree commit) and can carry the
>> fix as necessary. This is now fixed as far as linux-next is concerned,
>> but any non trivial conflicts should be mentioned to your upstream
>> maintainer when your tree is submitted for merging.  You may also want
>> to consider cooperating with the maintainer of the conflicting tree to
>> minimise any particularly complex conflicts.
>
> Hey All,
>
> what's the proper fix here?
>
> Roman,
>
> looks like adding mem_cgroup_usage() to include/linux/memcontrol.h
> wasn't really necessary, since kfuncs don't use it anyway?
> Should we just remove that line in bpf-next?

Yep. It was used in the previous version, but not in the latest one.

Just sent an official fix.

Thanks!