selftests/bpf: add test for softlock when modifying hashmap while iterating

Add test that modifies the map while it's being iterated in such a way that
hangs the kernel thread unless the _safe fix is applied to
bpf_for_each_hash_elem.

Signed-off-by: Brandon Kammerdiener <brandon.kammerdiener@intel.com>
Link: https://lore.kernel.org/r/20250424153246.141677-3-brandon.kammerdiener@intel.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>

diff --git a/tools/testing/selftests/bpf/prog_tests/for_each.c b/tools/testing/selftests/bpf/prog_tests/for_each.c
index 09f6487..5fea320 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/for_each.c
+++ b/tools/testing/selftests/bpf/prog_tests/for_each.c
@@ -6,6 +6,7 @@
 #include "for_each_array_map_elem.skel.h"
 #include "for_each_map_elem_write_key.skel.h"
 #include "for_each_multi_maps.skel.h"
+#include "for_each_hash_modify.skel.h"
 
 static unsigned int duration;
 
@@ -203,6 +204,40 @@ out:
        for_each_multi_maps__destroy(skel);
 }
 
+static void test_hash_modify(void)
+{
+       struct for_each_hash_modify *skel;
+       int max_entries, i, err;
+       __u64 key, val;
+
+       LIBBPF_OPTS(bpf_test_run_opts, topts,
+               .data_in = &pkt_v4,
+               .data_size_in = sizeof(pkt_v4),
+               .repeat = 1
+       );
+
+       skel = for_each_hash_modify__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "for_each_hash_modify__open_and_load"))
+               return;
+
+       max_entries = bpf_map__max_entries(skel->maps.hashmap);
+       for (i = 0; i < max_entries; i++) {
+               key = i;
+               val = i;
+               err = bpf_map__update_elem(skel->maps.hashmap, &key, sizeof(key),
+                                          &val, sizeof(val), BPF_ANY);
+               if (!ASSERT_OK(err, "map_update"))
+                       goto out;
+       }
+
+       err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_pkt_access), &topts);
+       ASSERT_OK(err, "bpf_prog_test_run_opts");
+       ASSERT_OK(topts.retval, "retval");
+
+out:
+       for_each_hash_modify__destroy(skel);
+}
+
 void test_for_each(void)
 {
        if (test__start_subtest("hash_map"))
@@ -213,4 +248,6 @@ void test_for_each(void)
                test_write_map_key();
        if (test__start_subtest("multi_maps"))
                test_multi_maps();
+       if (test__start_subtest("hash_modify"))
+               test_hash_modify();
 }

diff --git a/tools/testing/selftests/bpf/progs/for_each_hash_modify.c b/tools/testing/selftests/bpf/progs/for_each_hash_modify.c
new file mode 100644 (file)
index 0000000..8230716
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/for_each_hash_modify.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Intel Corporation */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+       __uint(type, BPF_MAP_TYPE_HASH);
+       __uint(max_entries, 128);
+       __type(key, __u64);
+       __type(value, __u64);
+} hashmap SEC(".maps");
+
+static int cb(struct bpf_map *map, __u64 *key, __u64 *val, void *arg)
+{
+       bpf_map_delete_elem(map, key);
+       bpf_map_update_elem(map, key, val, 0);
+       return 0;
+}
+
+SEC("tc")
+int test_pkt_access(struct __sk_buff *skb)
+{
+       (void)skb;
+
+       bpf_for_each_map_elem(&hashmap, cb, NULL, 0);
+
+       return 0;
+}