[PATCH] lib/bpf: Fix btf_load error lead to enable debug log

[PATCH] lib/bpf: Fix btf_load error lead to enable debug log

[Feng zhou]

From: Feng Zhou <zhoufeng.zf@bytedance.com>

Use tc with no verbose, when bpf_btf_attach fail,
the conditions:
"if (fd < 0 && (errno == ENOSPC || !ctx->log_size))"
will make ctx->log_size != 0. And then, bpf_prog_attach,
ctx->log_size != 0. so enable debug log.
The verifier log sometimes is so chatty on larger programs.
bpf_prog_attach is failed.
"Log buffer too small to dump verifier log 16777215 bytes (9 tries)!"

BTF load failure does not affect prog load. prog still work.
So when BTF/PROG load fail, enlarge log_size and re-fail with
having verbose.

Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 lib/bpf_legacy.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/bpf_legacy.c b/lib/bpf_legacy.c
index 8a03b9c2..d824388c 100644
--- a/lib/bpf_legacy.c
+++ b/lib/bpf_legacy.c
@@ -1531,7 +1531,7 @@ retry:
 		 * into our buffer. Still, try to give a debuggable error
 		 * log for the user, so enlarge it and re-fail.
 		 */
-		if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
+		if (fd < 0 && errno == ENOSPC) {
 			if (tries++ < 10 && !bpf_log_realloc(ctx))
 				goto retry;
 
@@ -2069,7 +2069,7 @@ retry:
 	fd = bpf_btf_load(ctx->btf_data->d_buf, ctx->btf_data->d_size,
 			  ctx->log, ctx->log_size);
 	if (fd < 0 || ctx->verbose) {
-		if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
+		if (fd < 0 && errno == ENOSPC) {
 			if (tries++ < 10 && !bpf_log_realloc(ctx))
 				goto retry;
 
-- 
2.11.0

Re: [PATCH] lib/bpf: Fix btf_load error lead to enable debug log

[Andrii Nakryiko]

On Wed, Jul 28, 2021 at 9:55 PM Feng zhou <zhoufeng.zf@bytedance.com> wrote:
>
> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>
> Use tc with no verbose, when bpf_btf_attach fail,
> the conditions:
> "if (fd < 0 && (errno == ENOSPC || !ctx->log_size))"
> will make ctx->log_size != 0. And then, bpf_prog_attach,
> ctx->log_size != 0. so enable debug log.
> The verifier log sometimes is so chatty on larger programs.
> bpf_prog_attach is failed.
> "Log buffer too small to dump verifier log 16777215 bytes (9 tries)!"
>
> BTF load failure does not affect prog load. prog still work.
> So when BTF/PROG load fail, enlarge log_size and re-fail with
> having verbose.
>
> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
> ---

This seems to be targeted against iproute2? It would be good to
specify that as [PATCH iproute2] or something.


>  lib/bpf_legacy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/bpf_legacy.c b/lib/bpf_legacy.c
> index 8a03b9c2..d824388c 100644
> --- a/lib/bpf_legacy.c
> +++ b/lib/bpf_legacy.c
> @@ -1531,7 +1531,7 @@ retry:
>                  * into our buffer. Still, try to give a debuggable error
>                  * log for the user, so enlarge it and re-fail.
>                  */
> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
> +               if (fd < 0 && errno == ENOSPC) {
>                         if (tries++ < 10 && !bpf_log_realloc(ctx))
>                                 goto retry;
>
> @@ -2069,7 +2069,7 @@ retry:
>         fd = bpf_btf_load(ctx->btf_data->d_buf, ctx->btf_data->d_size,
>                           ctx->log, ctx->log_size);
>         if (fd < 0 || ctx->verbose) {
> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
> +               if (fd < 0 && errno == ENOSPC) {
>                         if (tries++ < 10 && !bpf_log_realloc(ctx))
>                                 goto retry;
>
> --
> 2.11.0
>

Re: [External] Re: [PATCH] lib/bpf: Fix btf_load error lead to enable debug log

[zhoufeng]

在 2021/7/31 上午2:40, Andrii Nakryiko 写道:
> On Wed, Jul 28, 2021 at 9:55 PM Feng zhou <zhoufeng.zf@bytedance.com> wrote:
>>
>> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>>
>> Use tc with no verbose, when bpf_btf_attach fail,
>> the conditions:
>> "if (fd < 0 && (errno == ENOSPC || !ctx->log_size))"
>> will make ctx->log_size != 0. And then, bpf_prog_attach,
>> ctx->log_size != 0. so enable debug log.
>> The verifier log sometimes is so chatty on larger programs.
>> bpf_prog_attach is failed.
>> "Log buffer too small to dump verifier log 16777215 bytes (9 tries)!"
>>
>> BTF load failure does not affect prog load. prog still work.
>> So when BTF/PROG load fail, enlarge log_size and re-fail with
>> having verbose.
>>
>> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
>> ---
> 
> This seems to be targeted against iproute2? It would be good to
> specify that as [PATCH iproute2] or something.
> 
> 

Yeah, it's a good idea. I will resend it.


>>   lib/bpf_legacy.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/bpf_legacy.c b/lib/bpf_legacy.c
>> index 8a03b9c2..d824388c 100644
>> --- a/lib/bpf_legacy.c
>> +++ b/lib/bpf_legacy.c
>> @@ -1531,7 +1531,7 @@ retry:
>>                   * into our buffer. Still, try to give a debuggable error
>>                   * log for the user, so enlarge it and re-fail.
>>                   */
>> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
>> +               if (fd < 0 && errno == ENOSPC) {
>>                          if (tries++ < 10 && !bpf_log_realloc(ctx))
>>                                  goto retry;
>>
>> @@ -2069,7 +2069,7 @@ retry:
>>          fd = bpf_btf_load(ctx->btf_data->d_buf, ctx->btf_data->d_size,
>>                            ctx->log, ctx->log_size);
>>          if (fd < 0 || ctx->verbose) {
>> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
>> +               if (fd < 0 && errno == ENOSPC) {
>>                          if (tries++ < 10 && !bpf_log_realloc(ctx))
>>                                  goto retry;
>>
>> --
>> 2.11.0
>>