[v2,5/7] bpf: do not create bpf_non_sleepable_error_inject list when unnecessary

Commit Message

Vlastimil Babka June 19, 2024, 10:48 p.m. UTC

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 <[e-mail]>
---
 kernel/bpf/verifier.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

Comments

Alexei Starovoitov June 20, 2024, 1:18 a.m. UTC | #1

On Wed, Jun 19, 2024 at 3:49 PM Vlastimil Babka <[e-mail]> wrote:
>
> 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 <[e-mail]>
> ---
>  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.

Vlastimil Babka June 20, 2024, 8:15 a.m. UTC | #2

On 6/20/24 3:18 AM, Alexei Starovoitov wrote:
> On Wed, Jun 19, 2024 at 3:49 PM Vlastimil Babka <[e-mail]> wrote:
>>
>> 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 <[e-mail]>
>> ---
>>  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.

Patch

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
+
 int bpf_check_attach_target(struct bpf_verifier_log *log,
 			    const struct bpf_prog *prog,
 			    const struct bpf_prog *tgt_prog,