[v2] bpf: fix the xdp_adjust_tail sample prog issue

[v2] bpf: fix the xdp_adjust_tail sample prog issue

[Yuan Chen]

From: Yuan Chen <chenyuan@kylinos.cn>

During the xdp_adjust_tail test, probabilistic failure occurs and SKB package
is discarded by the kernel. After checking the issues by tracking SKB package,
it is identified that they were caused by checksum errors. Refer to checksum
of the arch/arm64/include/asm/checksum.h for fixing.

v2: Based on Alexei Starovoitov's suggestions, it is necessary to keep the code
 implementation consistent.

Fixes: c6ffd1ff7856 (bpf: add bpf_xdp_adjust_tail sample prog)
Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
---
 samples/bpf/xdp_adjust_tail_kern.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
index ffdd548627f0..da67bcad1c63 100644
--- a/samples/bpf/xdp_adjust_tail_kern.c
+++ b/samples/bpf/xdp_adjust_tail_kern.c
@@ -57,6 +57,7 @@ static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
 
 static __always_inline __u16 csum_fold_helper(__u32 csum)
 {
+	csum = (csum & 0xffff) + (csum >> 16);
 	return ~((csum & 0xffff) + (csum >> 16));
 }
 
-- 
2.46.0

Re: [v2] bpf: fix the xdp_adjust_tail sample prog issue

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Mon, 30 Sep 2024 10:41:15 +0800 you wrote:
> From: Yuan Chen <chenyuan@kylinos.cn>
> 
> During the xdp_adjust_tail test, probabilistic failure occurs and SKB package
> is discarded by the kernel. After checking the issues by tracking SKB package,
> it is identified that they were caused by checksum errors. Refer to checksum
> of the arch/arm64/include/asm/checksum.h for fixing.
> 
> [...]

Here is the summary with links:
  - [v2] bpf: fix the xdp_adjust_tail sample prog issue
    https://git.kernel.org/bpf/bpf-next/c/4236f114a3ff

You are awesome, thank you!
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