Re: [PATCH] selftests/bpf: trampoline_count: use dedicated target function

[Paul Chaignon]

On Sun, Mar 15, 2026 at 01:42:27PM +0800, Sun Jian wrote:
> trampoline_count fills all trampoline attachment slots for a single
> target function and verifies that one extra attach fails with -E2BIG.
> 
> It currently targets bpf_modify_return_test, which is also used by
> modify_return and get_func_ip_test. When those tests run in parallel,
> they can contend for the same per-function trampoline quota and
> cause unexpected attach failures. This issue is currently masked by
> harness serialization.
> 
> Add a dedicated bpf_trampoline_count_test target and switch
> trampoline_count to use it. This keeps the test semantics unchanged
> while isolating it from other modify_return-based selftests, so it no
> longer needs to run in serial mode. Remove the TODO comment as
> well.
> 
> Tested:
>   ./test_progs -t trampoline_count -vv
>   ./test_progs -t modify_return -vv
>   ./test_progs -t get_func_ip_test -vv
>   ./test_progs -j$(nproc) -t trampoline_count -vv
>   ./test_progs -j$(nproc) -t
>     trampoline_count,modify_return,get_func_ip_test -vv

I was able to reproduce the issue here then validate the fix. I however
had to include several more tests that use bpf_modify_return_test
(get_func_args_test, kprobe_multi_test, missed, and bpf_cookie) before
I could reliably reproduce (in a loop that runs until it fails with
an unexpected E2BIG).

Tested-by: Paul Chaignon <paul.chaignon@xxxxxxxxx>

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