selftests/bpf: Add bpf_{update, delete}_map_elem in hashmap iter program

Added bpf_{updata,delete}_map_elem to the very map element the
iter program is visiting. Due to rcu protection, the visited map
elements, although stale, should still contain correct values.
  $ ./test_progs -n 4/18
  #4/18 bpf_hash_map:OK
  #4 bpf_iter:OK
  Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@fb.com

diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_hash_map.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_hash_map.c
index 07ddbfd..6dfce3f 100644 (file)
--- a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_hash_map.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_hash_map.c
@@ -47,7 +47,10 @@ int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)
        __u32 seq_num = ctx->meta->seq_num;
        struct bpf_map *map = ctx->map;
        struct key_t *key = ctx->key;
+       struct key_t tmp_key;
        __u64 *val = ctx->value;
+       __u64 tmp_val = 0;
+       int ret;
 
        if (in_test_mode) {
                /* test mode is used by selftests to
@@ -61,6 +64,18 @@ int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)
                if (key == (void *)0 || val == (void *)0)
                        return 0;
 
+               /* update the value and then delete the <key, value> pair.
+                * it should not impact the existing 'val' which is still
+                * accessible under rcu.
+                */
+               __builtin_memcpy(&tmp_key, key, sizeof(struct key_t));
+               ret = bpf_map_update_elem(&hashmap1, &tmp_key, &tmp_val, 0);
+               if (ret)
+                       return 0;
+               ret = bpf_map_delete_elem(&hashmap1, &tmp_key);
+               if (ret)
+                       return 0;
+
                key_sum_a += key->a;
                key_sum_b += key->b;
                key_sum_c += key->c;