selftests/bpf: Fix htab_update/reenter_update selftest failure

Since commit 31158ad02ddb ("rqspinlock: Add deadlock detection
and recovery") the updated path on re-entrancy now reports deadlock
via -EDEADLK instead of the previous -EBUSY.

Also, the way reentrancy was exercised (via fentry/lookup_elem_raw)
has been fragile because lookup_elem_raw may be inlined
(find_kernel_btf_id() will return -ESRCH).

To fix this fentry is attached to bpf_obj_free_fields() instead of
lookup_elem_raw() and:

- The htab map is made to use a BTF-described struct val with a
  struct bpf_timer so that check_and_free_fields() reliably calls
  bpf_obj_free_fields() on element replacement.

- The selftest is updated to do two updates to the same key (insert +
  replace) in prog_test.

- The selftest is updated to align with expected errno with the
  kernel’s current behavior.

Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Link: https://lore.kernel.org/r/20251117060752.129648-1-skb99@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 13 insertions, 6 deletions

diff --git a/tools/testing/selftests/bpf/progs/htab_update.c b/tools/testing/selftests/bpf/progs/htab_update.c
index 7481bb30b29b..195d3b2fba00 100644
--- a/tools/testing/selftests/bpf/progs/htab_update.c
+++ b/tools/testing/selftests/bpf/progs/htab_update.c
@@ -6,24 +6,31 @@
 
 char _license[] SEC("license") = "GPL";
 
+/* Map value type: has BTF-managed field (bpf_timer) */
+struct val {
+	struct bpf_timer t;
+	__u64 payload;
+};
+
 struct {
 	__uint(type, BPF_MAP_TYPE_HASH);
 	__uint(max_entries, 1);
-	__uint(key_size, sizeof(__u32));
-	__uint(value_size, sizeof(__u32));
+	__type(key, __u32);
+	__type(value, struct val);
 } htab SEC(".maps");
 
 int pid = 0;
 int update_err = 0;
 
-SEC("?fentry/lookup_elem_raw")
-int lookup_elem_raw(void *ctx)
+SEC("?fentry/bpf_obj_free_fields")
+int bpf_obj_free_fields(void *ctx)
 {
-	__u32 key = 0, value = 1;
+	__u32 key = 0;
+	struct val value = { .payload = 1 };
 
 	if ((bpf_get_current_pid_tgid() >> 32) != pid)
 		return 0;
 
-	update_err = bpf_map_update_elem(&htab, &key, &value, 0);
+	update_err = bpf_map_update_elem(&htab, &key, &value, BPF_ANY);
 	return 0;
 }