bpf: Convert bpf_selem_link_map to failable

To prepare for changing bpf_local_storage_map_bucket::lock to rqspinlock,
convert bpf_selem_link_map() to failable. It still always succeeds and
returns 0 until the change happens. No functional change.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20260205222916.1788211-4-ameryhung@gmail.com

Author: ameryhung

include/linux/bpf_local_storage.h

@@ -178,9 +178,9 @@ void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
 
 void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now);
 
-void bpf_selem_link_map(struct bpf_local_storage_map *smap,
-			struct bpf_local_storage *local_storage,
-			struct bpf_local_storage_elem *selem);
+int bpf_selem_link_map(struct bpf_local_storage_map *smap,
+		       struct bpf_local_storage *local_storage,
+		       struct bpf_local_storage_elem *selem);
 
 struct bpf_local_storage_elem *
 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner, void *value,

kernel/bpf/bpf_local_storage.c

@@ -365,9 +365,9 @@ static void bpf_selem_unlink_map_nolock(struct bpf_local_storage_elem *selem)
 	hlist_del_init_rcu(&selem->map_node);
 }
 
-void bpf_selem_link_map(struct bpf_local_storage_map *smap,
-			struct bpf_local_storage *local_storage,
-			struct bpf_local_storage_elem *selem)
+int bpf_selem_link_map(struct bpf_local_storage_map *smap,
+		       struct bpf_local_storage *local_storage,
+		       struct bpf_local_storage_elem *selem)
 {
 	struct bpf_local_storage_map_bucket *b;
 	unsigned long flags;
@@ -376,6 +376,8 @@ void bpf_selem_link_map(struct bpf_local_storage_map *smap,
 	raw_spin_lock_irqsave(&b->lock, flags);
 	hlist_add_head_rcu(&selem->map_node, &b->list);
 	raw_spin_unlock_irqrestore(&b->lock, flags);
+
+	return 0;
 }
 
 static void bpf_selem_link_map_nolock(struct bpf_local_storage_map_bucket *b,

net/core/bpf_sk_storage.c

@@ -191,7 +191,14 @@ int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
 		}
 
 		if (new_sk_storage) {
-			bpf_selem_link_map(smap, new_sk_storage, copy_selem);
+			ret = bpf_selem_link_map(smap, new_sk_storage, copy_selem);
+			if (ret) {
+				bpf_selem_free(copy_selem, true);
+				atomic_sub(smap->elem_size,
+					   &newsk->sk_omem_alloc);
+				bpf_map_put(map);
+				goto out;
+			}
 			bpf_selem_link_storage_nolock(new_sk_storage, copy_selem);
 		} else {
 			ret = bpf_local_storage_alloc(newsk, smap, copy_selem, GFP_ATOMIC);