Re: [PATCH bpf-next 4/4] selftests/bpf: Fix a user_ringbuf failure with arm64 64KB page size

[Yonghong Song <yonghong.song@linux.dev>]

On 6/5/25 8:23 PM, Yonghong Song wrote:
> The ringbuf max_entries must be PAGE_ALIGNED. See kernel function
> ringbuf_map_alloc(). So for arm64 64KB page size, adjust max_entries
> properly.
>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
>   tools/testing/selftests/bpf/prog_tests/user_ringbuf.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
> index d424e7ecbd12..f50aa8e7f6c2 100644
> --- a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
> @@ -21,8 +21,7 @@
>   #include "../progs/test_user_ringbuf.h"
>   
>   static const long c_sample_size = sizeof(struct sample) + BPF_RINGBUF_HDR_SZ;
> -static const long c_ringbuf_size = 1 << 12; /* 1 small page */
> -static const long c_max_entries = c_ringbuf_size / c_sample_size;
> +static long c_ringbuf_size, c_max_entries;
>   
>   static void drain_current_samples(void)
>   {
> @@ -686,6 +685,9 @@ void test_user_ringbuf(void)
>   {
>   	int i;
>   
> +	c_ringbuf_size = getpagesize(); /* 1 page */
> +	c_max_entries = c_ringbuf_size / c_sample_size;
> +
>   	for (i = 0; i < ARRAY_SIZE(success_tests); i++) {
>   		if (!test__start_subtest(success_tests[i].test_name))
>   			continue;

CI reports a build failure error:

/tmp/work/bpf/bpf/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c:426:2: 
error: call to '__compiletime_assert_0' declared with 'error' attribute: 
BUILD_BUG_ON failed: total_samples <= c_max_entries   426 | BUILD_BUG_ON(total_samples <= c_max_entries     |

/tmp/work/bpf/bpf/tools/include/linux/build_bug.h:50:2: note: expanded 
from macro 'BUILD_BUG_ON' 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON 
failed: " #condition) | ^ 
/tmp/work/bpf/bpf/tools/include/linux/build_bug.h:39:37: note: expanded 
from macro 'BUILD_BUG_ON_MSG' 39 | #define BUILD_BUG_ON_MSG(cond, msg) 
compiletime_assert(!(cond), msg) | ^ 
/tmp/work/bpf/bpf/tools/include/linux/compiler.h:37:2: note: expanded 
from macro 'compiletime_assert' 37 | _compiletime_assert(condition, msg, 
__compiletime_assert_, __COUNTER__) | ^ 
/tmp/work/bpf/bpf/tools/include/linux/compiler.h:25:2: note: expanded 
from macro '_compiletime_assert' 25 | __compiletime_assert(condition, 
msg, prefix, suffix) | ^ 
/tmp/work/bpf/bpf/tools/include/linux/compiler.h:18:4: note: expanded 
from macro '__compiletime_assert' 18 | prefix ## suffix(); \ | ^ 
<scratch space>:60:1: note: expanded from here 60 | __compiletime_assert_0

| ^ This happens for the release build (RELEASE=1 in build command line 
where -O2 is used in stead of -O0). Converting the BUILD_BUG_ON to 
ASSERT can fix the problem. diff --git 
a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c 
b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c index 
f50aa8e7f6c2..467b5b8beecc 100644 --- 
a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c +++ 
b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c @@ -423,7 +423,9 
@@ static void test_user_ringbuf_loop(void) uint32_t remaining_samples = 
total_samples; int err; - BUILD_BUG_ON(total_samples <= c_max_entries); 
+ if (!ASSERT_LE(total_samples, c_max_entries, "compare_c_max_entries")) 
+ return; + err = load_skel_create_user_ringbuf(&skel, &ringbuf); I will 
wait for some further comments before posting v2.