Re: [PATCH v4 bpf-next 6/7] selftests/bpf: Test BTF sysfs inline representations

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] selftests: flaky test in test_btf_inline_sysfs_all() due to missing -ENOENT check
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commit df90a8288d824aad2169294b18c9baff7baa8c42
Author: Alan Maguire <alan.maguire@oracle.com>

selftests/bpf: Test BTF sysfs inline representations

This commit adds tests to load vmlinux, vmlinux.inline, and module entries
from /sys/fs/btf to sanity-check inline representations and kernel
relocations. It also tests mmap functionality for vmlinux.inline.

> diff --git a/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
> --- a/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
> +++ b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c

[ ... ]

> +static void test_btf_inline_sysfs_all(void)
> +{

[ ... ]

> +	while ((dentry = readdir(dir)) != NULL) {

[ ... ]

> +		if (!base_btf) {
> +			module_btf = btf__parse_split(btf_path, vmlinux_btf);
> +			err = libbpf_get_error(module_btf);
> +			if (err) {
> +				/* A module can be unloaded while its sysfs entry is iterated. */
> +				if (err == -ENOENT)
> +					continue;
> +				ASSERT_OK(err, "parse_module_btf");
> +				continue;
> +			}
> +			base_btf = module_btf;
> +		}
> +		if (stat(inline_path, &st)) {
> +			err = errno;
> +			if (err != ENOENT)
> +				ASSERT_OK(err, "stat_inline_btf");
> +			btf__free(module_btf);
> +			continue;
> +		}
> +		if (base_btf == vmlinux_btf)
> +			test_btf_mmap_sysfs(inline_path, base_btf);
> +		inline_btf = btf__parse_split(inline_path, base_btf);
> +		err = libbpf_get_error(inline_btf);
> +		if (!err)
> +			btf__free(inline_btf);
> +		ASSERT_OK(err, "parse_inline_btf");

[Severity: Medium]
Is this ASSERT_OK() missing a check for -ENOENT?

When parsing the module BTF earlier in the loop, the code correctly handles
the case where a module is unloaded during sysfs iteration by checking for
-ENOENT.

However, a time-of-check to time-of-use race can occur here. If the module
is unloaded in the small window between stat() and btf__parse_split(), the
parse function will return -ENOENT. This causes ASSERT_OK() to fail and
could lead to flaky tests in parallel testing environments.

> +		btf__free(module_btf);
> +	}
> +	closedir(dir);
> +
> +	btf__free(vmlinux_btf);
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20261009112324.1442319-1-alan.maguire@oracle.com?part=6