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

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Message-ID: <CAADnVQKkphWpwKE17bGQao36dH8xqCyV-iXDcagrO7s-VOPE-w@mail.gmail.com>
Date: Mon, 5 Jan 2026 18:15:36 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, bpf <bpf@...r.kernel.org>, 
	Networking <netdev@...r.kernel.org>, Chen Ridong <chenridong@...wei.com>, 
	JP Kobryn <inwardvessel@...il.com>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	Linux Next Mailing List <linux-next@...r.kernel.org>, Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: linux-next: manual merge of the bpf-next tree with the
 mm-unstable tree

On Sun, Jan 4, 2026 at 6:04 PM Stephen Rothwell <sfr@...b.auug.org.au> 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?

Just:
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6a5d65487b70..229ac9835adb 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -950,7 +950,6 @@ static inline void mod_memcg_page_state(struct page *page,
 }

 unsigned long memcg_events(struct mem_cgroup *memcg, int event);
-unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
 unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx);
 unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item);
 bool memcg_stat_item_valid(int idx);

compiles fine.

If you agree pls send an official patch.