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

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Message-Id: <20210729045516.7373-1-zhoufeng.zf@bytedance.com>
Date:   Thu, 29 Jul 2021 12:55:16 +0800
From:   Feng zhou <zhoufeng.zf@...edance.com>
To:     netdev@...r.kernel.org
Cc:     stephen@...workplumber.org, kuznet@....inr.ac.ru,
        duanxiongchun@...edance.com, wangdongdong.6@...edance.com,
        chenzhuowen.simon@...edance.com, zhoufeng.zf@...edance.com
Subject: [PATCH] lib/bpf: Fix btf_load error lead to enable debug log

From: Feng Zhou <zhoufeng.zf@...edance.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@...edance.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