We're seeing the following new warnings on netdev/build_32bit and
netdev/build_allmodconfig_warn CI jobs:

    ../net/core/filter.c:8608:1: warning: symbol
    'nf_conn_btf_access_lock' was not declared. Should it be static?
    ../net/core/filter.c:8611:5: warning: symbol 'nfct_bsa' was not
    declared. Should it be static?

Fix by ensuring extern declaration is present while compiling filter.o.

Fixes: 864b656f82cc ("bpf: Add support for writing to nf_conn:mark")
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 include/linux/filter.h                   | 6 ++++++
 include/net/netfilter/nf_conntrack_bpf.h | 6 ------
 net/netfilter/nf_conntrack_bpf.c         | 1 +
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 75335432fcbc..98e28126c24b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -567,6 +567,12 @@ struct sk_filter {
 
 DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 
+extern struct mutex nf_conn_btf_access_lock;
+extern int (*nfct_btf_struct_access)(struct bpf_verifier_log *log, const struct btf *btf,
+				     const struct btf_type *t, int off, int size,
+				     enum bpf_access_type atype, u32 *next_btf_id,
+				     enum bpf_type_flag *flag);
+
 typedef unsigned int (*bpf_dispatcher_fn)(const void *ctx,
 					  const struct bpf_insn *insnsi,
 					  unsigned int (*bpf_func)(const void *,
diff --git a/include/net/netfilter/nf_conntrack_bpf.h b/include/net/netfilter/nf_conntrack_bpf.h
index 1199d4f8e019..e1f1ba3116ef 100644
--- a/include/net/netfilter/nf_conntrack_bpf.h
+++ b/include/net/netfilter/nf_conntrack_bpf.h
@@ -12,12 +12,6 @@
 extern int register_nf_conntrack_bpf(void);
 extern void cleanup_nf_conntrack_bpf(void);
 
-extern struct mutex nf_conn_btf_access_lock;
-extern int (*nfct_btf_struct_access)(struct bpf_verifier_log *log, const struct btf *btf,
-				     const struct btf_type *t, int off, int size,
-				     enum bpf_access_type atype, u32 *next_btf_id,
-				     enum bpf_type_flag *flag);
-
 #else
 
 static inline int register_nf_conntrack_bpf(void)
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index 29c4efb3da5e..67df64283aef 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -9,6 +9,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/bpf.h>
 #include <linux/btf.h>
+#include <linux/filter.h>
 #include <linux/mutex.h>
 #include <linux/types.h>
 #include <linux/btf_ids.h>
-- 
2.37.1

On 9/20/22 7:15 AM, Daniel Xu wrote:
> --- a/include/net/netfilter/nf_conntrack_bpf.h
> +++ b/include/net/netfilter/nf_conntrack_bpf.h
> @@ -12,12 +12,6 @@
>   extern int register_nf_conntrack_bpf(void);
>   extern void cleanup_nf_conntrack_bpf(void);
>   
> -extern struct mutex nf_conn_btf_access_lock;
> -extern int (*nfct_btf_struct_access)(struct bpf_verifier_log *log, const struct btf *btf,
> -				     const struct btf_type *t, int off, int size,
> -				     enum bpf_access_type atype, u32 *next_btf_id,
> -				     enum bpf_type_flag *flag);
> -

I removed the 'include mutex.h' from this header and applied.  Thanks.