Merge branch 'percpu_hash-maps'

Leon Hwang says:

====================
In the discussion thread
"[PATCH bpf-next v9 0/7] bpf: Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags for percpu maps"[1],
it was pointed out that missing calls to bpf_obj_free_fields() could
lead to memory leaks.

A selftest was added to confirm that this is indeed a real issue - the
refcount of BPF_KPTR_REF field is not decremented when
bpf_obj_free_fields() is missing after copy_map_value[,_long]().

Further inspection of copy_map_value[,_long]() call sites revealed two
locations affected by this issue:

1. pcpu_copy_value()
2. htab_map_update_elem() when used with BPF_F_LOCK

Similar case happens when update local storage maps with BPF_F_LOCK.

This series fixes the cases where BPF_F_LOCK is not involved by
properly calling bpf_obj_free_fields() after copy_map_value[,_long](),
and adds a selftest to verify the fix.

The remaining cases involving BPF_F_LOCK will be addressed in a
separate patch set after the series
"bpf: Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags for percpu maps"
is applied.

Changes:
v5 -> v6:
* Update the test name to include "refcounted_kptr".
* Update some local variables' name in the test (per Alexei).
* v5: https://lore.kernel.org/bpf/20251104142714.99878-1-leon.hwang@linux.dev/

v4 -> v5:
* Use a local variable to store the this_cpu_ptr()/per_cpu_ptr() result,
  and reuse it between copy_map_value[,_long]() and
  bpf_obj_free_fields() in patch #1 (per Andrii).
* Drop patch #2 and #3, because the combination of BPF_F_LOCK with other
  special fields (except for BPF_SPIN_LOCK) will be disallowed on the
  UAPI side in the future (per Alexei).
* v4: https://lore.kernel.org/bpf/20251030152451.62778-1-leon.hwang@linux.dev/

v3 -> v4:
* Target bpf-next tree.
* Address comments from Amery:
  * Drop 'bpf_obj_free_fields()' in the path of updating local storage
    maps without BPF_F_LOCK.
  * Drop the corresponding self test.
  * Respin the other test of local storage maps using syscall BPF
    programs.
* v3: https://lore.kernel.org/bpf/20251026154000.34151-1-leon.hwang@linux.dev/

v2 -> v3:
* Free special fields when update local storage maps without BPF_F_LOCK.
* Add test to verify decrementing refcount when update cgroup local
  storage maps without BPF_F_LOCK.
* Address review from AI bot:
  * Slow path with BPF_F_LOCK (around line 642-646) in
    'bpf_local_storage.c'.
* v2: https://lore.kernel.org/bpf/20251020164608.20536-1-leon.hwang@linux.dev/

v1 -> v2:
* Add test to verify decrementing refcount when update cgroup local
  storage maps with BPF_F_LOCK.
* Address review from AI bot:
  * Fast path without bucket lock (around line 610) in
    'bpf_local_storage.c'.
* v1: https://lore.kernel.org/bpf/20251016145801.47552-1-leon.hwang@linux.dev/
====================

Link: https://patch.msgid.link/20251105151407.12723-1-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

kernel/bpf/hashtab.c

@@ -934,15 +934,21 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 static void pcpu_copy_value(struct bpf_htab *htab, void __percpu *pptr,
 			    void *value, bool onallcpus)
 {
+	void *ptr;
+
 	if (!onallcpus) {
 		/* copy true value_size bytes */
-		copy_map_value(&htab->map, this_cpu_ptr(pptr), value);
+		ptr = this_cpu_ptr(pptr);
+		copy_map_value(&htab->map, ptr, value);
+		bpf_obj_free_fields(htab->map.record, ptr);
 	} else {
 		u32 size = round_up(htab->map.value_size, 8);
 		int off = 0, cpu;
 
 		for_each_possible_cpu(cpu) {
-			copy_map_value_long(&htab->map, per_cpu_ptr(pptr, cpu), value + off);
+			ptr = per_cpu_ptr(pptr, cpu);
+			copy_map_value_long(&htab->map, ptr, value + off);
+			bpf_obj_free_fields(htab->map.record, ptr);
 			off += size;
 		}
 	}

tools/testing/selftests/bpf/prog_tests/refcounted_kptr.c

@@ -44,3 +44,59 @@ void test_refcounted_kptr_wrong_owner(void)
 	ASSERT_OK(opts.retval, "rbtree_wrong_owner_remove_fail_a2 retval");
 	refcounted_kptr__destroy(skel);
 }
+
+void test_percpu_hash_refcounted_kptr_refcount_leak(void)
+{
+	struct refcounted_kptr *skel;
+	int cpu_nr, fd, err, key = 0;
+	struct bpf_map *map;
+	size_t values_sz;
+	u64 *values;
+	LIBBPF_OPTS(bpf_test_run_opts, opts,
+		    .data_in = &pkt_v4,
+		    .data_size_in = sizeof(pkt_v4),
+		    .repeat = 1,
+	);
+
+	cpu_nr = libbpf_num_possible_cpus();
+	if (!ASSERT_GT(cpu_nr, 0, "libbpf_num_possible_cpus"))
+		return;
+
+	values = calloc(cpu_nr, sizeof(u64));
+	if (!ASSERT_OK_PTR(values, "calloc values"))
+		return;
+
+	skel = refcounted_kptr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "refcounted_kptr__open_and_load")) {
+		free(values);
+		return;
+	}
+
+	values_sz = cpu_nr * sizeof(u64);
+	memset(values, 0, values_sz);
+
+	map = skel->maps.percpu_hash;
+	err = bpf_map__update_elem(map, &key, sizeof(key), values, values_sz, 0);
+	if (!ASSERT_OK(err, "bpf_map__update_elem"))
+		goto out;
+
+	fd = bpf_program__fd(skel->progs.percpu_hash_refcount_leak);
+	err = bpf_prog_test_run_opts(fd, &opts);
+	if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
+		goto out;
+	if (!ASSERT_EQ(opts.retval, 2, "opts.retval"))
+		goto out;
+
+	err = bpf_map__update_elem(map, &key, sizeof(key), values, values_sz, 0);
+	if (!ASSERT_OK(err, "bpf_map__update_elem"))
+		goto out;
+
+	fd = bpf_program__fd(skel->progs.check_percpu_hash_refcount);
+	err = bpf_prog_test_run_opts(fd, &opts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+	ASSERT_EQ(opts.retval, 1, "opts.retval");
+
+out:
+	refcounted_kptr__destroy(skel);
+	free(values);
+}

tools/testing/selftests/bpf/progs/refcounted_kptr.c

@@ -568,4 +568,64 @@ int BPF_PROG(rbtree_sleepable_rcu_no_explicit_rcu_lock,
 	return 0;
 }
 
+private(kptr_ref) u64 ref;
+
+static int probe_read_refcount(void)
+{
+	u32 refcount;
+
+	bpf_probe_read_kernel(&refcount, sizeof(refcount), (void *) ref);
+	return refcount;
+}
+
+static int __insert_in_list(struct bpf_list_head *head, struct bpf_spin_lock *lock,
+			    struct node_data __kptr **node)
+{
+	struct node_data *node_new, *node_ref, *node_old;
+
+	node_new = bpf_obj_new(typeof(*node_new));
+	if (!node_new)
+		return -1;
+
+	node_ref = bpf_refcount_acquire(node_new);
+	node_old = bpf_kptr_xchg(node, node_new);
+	if (node_old) {
+		bpf_obj_drop(node_old);
+		bpf_obj_drop(node_ref);
+		return -2;
+	}
+
+	bpf_spin_lock(lock);
+	bpf_list_push_front(head, &node_ref->l);
+	ref = (u64)(void *) &node_ref->ref;
+	bpf_spin_unlock(lock);
+	return probe_read_refcount();
+}
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_HASH);
+	__type(key, int);
+	__type(value, struct map_value);
+	__uint(max_entries, 1);
+} percpu_hash SEC(".maps");
+
+SEC("tc")
+int percpu_hash_refcount_leak(void *ctx)
+{
+	struct map_value *v;
+	int key = 0;
+
+	v = bpf_map_lookup_elem(&percpu_hash, &key);
+	if (!v)
+		return 0;
+
+	return __insert_in_list(&head, &lock, &v->node);
+}
+
+SEC("tc")
+int check_percpu_hash_refcount(void *ctx)
+{
+	return probe_read_refcount();
+}
+
 char _license[] SEC("license") = "GPL";