On 6/20/24 3:18 AM, Alexei Starovoitov wrote:

On Wed, Jun 19, 2024 at 3:49 PM Vlastimil Babka [off-list ref] wrote:

quoted

When CONFIG_FUNCTION_ERROR_INJECTION is disabled,
within_error_injection_list() will return false for any address and the
result of check_non_sleepable_error_inject() denylist is thus redundant.
The bpf_non_sleepable_error_inject list thus does not need to be
constructed at all, so #ifdef it out.

This will allow to inline functions on the list when
CONFIG_FUNCTION_ERROR_INJECTION is disabled as there will be no BTF_ID()
reference for them.

Signed-off-by: Vlastimil Babka <redacted>
---
 kernel/bpf/verifier.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 77da1f438bec..5cd93de37d68 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -21044,6 +21044,8 @@ static int check_attach_modify_return(unsigned long addr, const char *func_name)
        return -EINVAL;
 }

+#ifdef CONFIG_FUNCTION_ERROR_INJECTION
+
 /* list of non-sleepable functions that are otherwise on
  * ALLOW_ERROR_INJECTION list
  */

@@ -21061,6 +21063,19 @@ static int check_non_sleepable_error_inject(u32 btf_id)
        return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
 }

+#else /* CONFIG_FUNCTION_ERROR_INJECTION */
+
+/*
+ * Pretend the denylist is empty, within_error_injection_list() will return
+ * false anyway.
+ */
+static int check_non_sleepable_error_inject(u32 btf_id)
+{
+       return 0;
+}
+
+#endif

The comment reads like this is an optimization, but it's a mandatory
ifdef since should_failslab() might not be found by resolve_btfid
during the build.
Please make it clear in the comment.

The comment just tried to explain why the return value is 0 and not 1 (which
would be also somewhat logical) but ok, will make it more clear.