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.

Open code bpf_selem_unlink_storage() in the only caller,
bpf_selem_unlink(), since unlink_map and unlink_storage must be done
together after all the necessary locks are acquired.

For bpf_local_storage_map_free(), ignore the return from
bpf_selem_unlink() for now. A later patch will allow it to unlink selems
even when failing to acquire locks.

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/20260205222916.1788211-5-ameryhung@gmail.com

Author: ameryhung

include/linux/bpf_local_storage.h

@@ -176,7 +176,7 @@ 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 *local_storage,

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)

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)

kernel/bpf/bpf_local_storage.c

@@ -308,33 +308,6 @@ static bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_stor
 	return free_local_storage;
 }
 
-static void bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem,
-				     bool reuse_now)
-{
-	struct bpf_local_storage *local_storage;
-	bool free_local_storage = false;
-	HLIST_HEAD(selem_free_list);
-	unsigned long flags;
-
-	if (unlikely(!selem_linked_to_storage_lockless(selem)))
-		/* selem has already been unlinked from sk */
-		return;
-
-	local_storage = rcu_dereference_check(selem->local_storage,
-					      bpf_rcu_lock_held());
-
-	raw_spin_lock_irqsave(&local_storage->lock, flags);
-	if (likely(selem_linked_to_storage(selem)))
-		free_local_storage = bpf_selem_unlink_storage_nolock(
-			local_storage, selem, &selem_free_list);
-	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
-
-	bpf_selem_free_list(&selem_free_list, reuse_now);
-
-	if (free_local_storage)
-		bpf_local_storage_free(local_storage, reuse_now);
-}
-
 void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
 				   struct bpf_local_storage_elem *selem)
 {
@@ -386,19 +359,43 @@ static void bpf_selem_link_map_nolock(struct bpf_local_storage_map_bucket *b,
 	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)
 {
-	int err;
+	struct bpf_local_storage *local_storage;
+	bool free_local_storage = false;
+	HLIST_HEAD(selem_free_list);
+	unsigned long flags;
+	int err = 0;
 
-	/* Always unlink from map before unlinking from local_storage
-	 * because selem will be freed after successfully unlinked from
-	 * the local_storage.
-	 */
-	err = bpf_selem_unlink_map(selem);
-	if (err)
-		return;
+	if (unlikely(!selem_linked_to_storage_lockless(selem)))
+		/* selem has already been unlinked from sk */
+		return 0;
+
+	local_storage = rcu_dereference_check(selem->local_storage,
+					      bpf_rcu_lock_held());
+
+	raw_spin_lock_irqsave(&local_storage->lock, flags);
+	if (likely(selem_linked_to_storage(selem))) {
+		/* Always unlink from map before unlinking from local_storage
+		 * because selem will be freed after successfully unlinked from
+		 * the local_storage.
+		 */
+		err = bpf_selem_unlink_map(selem);
+		if (err)
+			goto out;
+
+		free_local_storage = bpf_selem_unlink_storage_nolock(
+			local_storage, selem, &selem_free_list);
+	}
+out:
+	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 
-	bpf_selem_unlink_storage(selem, reuse_now);
+	bpf_selem_free_list(&selem_free_list, reuse_now);
+
+	if (free_local_storage)
+		bpf_local_storage_free(local_storage, reuse_now);
+
+	return err;
 }
 
 void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,

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)

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() */