netdev - [RFC PATCH bpf-next v2 05/12] bpf: Convert bpf_selem

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Message-ID: <20251002225356.1505480-6-ameryhung@gmail.com>
Date: Thu,  2 Oct 2025 15:53:44 -0700
From: Amery Hung <ameryhung@...il.com>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org,
	alexei.starovoitov@...il.com,
	andrii@...nel.org,
	daniel@...earbox.net,
	memxor@...il.com,
	martin.lau@...nel.org,
	kpsingh@...nel.org,
	yonghong.song@...ux.dev,
	song@...nel.org,
	haoluo@...gle.com,
	ameryhung@...il.com,
	kernel-team@...a.com
Subject: [RFC PATCH bpf-next v2 05/12] bpf: Convert bpf_selem_unlink to failable

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

For bpf_local_storage_map_free(), since it cannot deadlock with itself
or bpf_local_storage_destroy who the function might be racing with,
retry if bpf_selem_unlink() fails due to rqspinlock returning errors.

__must_check is added to the function declaration locally to make sure
all callers are accounted for during the conversion.

Signed-off-by: Amery Hung <ameryhung@...il.com>
---
 include/linux/bpf_local_storage.h | 2 +-
 kernel/bpf/bpf_cgrp_storage.c     | 3 +--
 kernel/bpf/bpf_inode_storage.c    | 4 +---
 kernel/bpf/bpf_local_storage.c    | 6 ++++--
 kernel/bpf/bpf_task_storage.c     | 4 +---
 net/core/bpf_sk_storage.c         | 4 +---
 6 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h
index dc56fa459ac9..26b7f53dad33 100644
--- a/include/linux/bpf_local_storage.h
+++ b/include/linux/bpf_local_storage.h
@@ -180,7 +180,7 @@ int bpf_local_storage_map_check_btf(const struct bpf_map *map,
 void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
 				   struct bpf_local_storage_elem *selem);
 
-void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now);
+int bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now);
 
 int bpf_selem_link_map(struct bpf_local_storage_map *smap,
 		       struct bpf_local_storage_elem *selem);
diff --git a/kernel/bpf/bpf_cgrp_storage.c b/kernel/bpf/bpf_cgrp_storage.c
index 0687a760974a..8fef24fcac68 100644
--- a/kernel/bpf/bpf_cgrp_storage.c
+++ b/kernel/bpf/bpf_cgrp_storage.c
@@ -118,8 +118,7 @@ static int cgroup_storage_delete(struct cgroup *cgroup, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata), false);
-	return 0;
+	return bpf_selem_unlink(SELEM(sdata), false);
 }
 
 static long bpf_cgrp_storage_delete_elem(struct bpf_map *map, void *key)
diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
index e54cce2b9175..cedc99184dad 100644
--- a/kernel/bpf/bpf_inode_storage.c
+++ b/kernel/bpf/bpf_inode_storage.c
@@ -110,9 +110,7 @@ static int inode_storage_delete(struct inode *inode, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata), false);
-
-	return 0;
+	return bpf_selem_unlink(SELEM(sdata), false);
 }
 
 static long bpf_fd_inode_storage_delete_elem(struct bpf_map *map, void *key)
diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 9c2b041ae9ca..e0e405060e3c 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -433,7 +433,7 @@ static void bpf_selem_link_map_nolock(struct bpf_local_storage_map *smap,
 	hlist_add_head_rcu(&selem->map_node, &b->list);
 }
 
-void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now)
+int bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now)
 {
 	struct bpf_local_storage_map *storage_smap;
 	struct bpf_local_storage *local_storage;
@@ -472,6 +472,8 @@ void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now)
 
 	if (free_local_storage)
 		bpf_local_storage_free(local_storage, storage_smap, bpf_ma, reuse_now);
+
+	return 0;
 }
 
 void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
@@ -930,7 +932,7 @@ void bpf_local_storage_map_free(struct bpf_map *map,
 				struct bpf_local_storage_elem, map_node))) {
 			if (busy_counter)
 				this_cpu_inc(*busy_counter);
-			bpf_selem_unlink(selem, true);
+			while (bpf_selem_unlink(selem, true));
 			if (busy_counter)
 				this_cpu_dec(*busy_counter);
 			cond_resched_rcu();
diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
index a1dc1bf0848a..ab902364ac23 100644
--- a/kernel/bpf/bpf_task_storage.c
+++ b/kernel/bpf/bpf_task_storage.c
@@ -167,9 +167,7 @@ static int task_storage_delete(struct task_struct *task, struct bpf_map *map,
 	if (!nobusy)
 		return -EBUSY;
 
-	bpf_selem_unlink(SELEM(sdata), false);
-
-	return 0;
+	return bpf_selem_unlink(SELEM(sdata), false);
 }
 
 static long bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index fac5cf385785..7b3d44667cee 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -40,9 +40,7 @@ static int bpf_sk_storage_del(struct sock *sk, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata), false);
-
-	return 0;
+	return bpf_selem_unlink(SELEM(sdata), false);
 }
 
 /* Called by __sk_destruct() & bpf_sk_storage_clone() */
-- 
2.47.3