bpf: Fix the xdp_adjust_tail sample prog issue

[ Upstream commit 4236f114a3ffbbfd217436c08852e94cae372f57 ]

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240930024115.52841-1-chenyuan_fl@163.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
index 411fdb21f8bcf62efac06bdf8a80997e3615c7f5..9783754bdd8bb142fb4ffbaaff4dd0afed686c1d 100644 (file)
--- a/samples/bpf/xdp_adjust_tail_kern.c
+++ b/samples/bpf/xdp_adjust_tail_kern.c
@@ -54,6 +54,7 @@ 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));
 }