Re: [RFC/PATCH bpf-next 3/3] selftests/bpf: Add a test for kmem_cache_iter

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Sep 27, 2024 at 11:41:33AM -0700, Namhyung Kim wrote:
> The test traverses all slab caches using the kmem_cache_iter and check
> if current task's pointer is from "task_struct" slab cache.
> 
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  .../bpf/prog_tests/kmem_cache_iter.c          | 64 ++++++++++++++++++
>  tools/testing/selftests/bpf/progs/bpf_iter.h  |  7 ++
>  .../selftests/bpf/progs/kmem_cache_iter.c     | 66 +++++++++++++++++++
>  3 files changed, 137 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> new file mode 100644
> index 0000000000000000..814bcc453e9f3ccd
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> @@ -0,0 +1,64 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Google */
> +
> +#include <test_progs.h>
> +#include <bpf/libbpf.h>
> +#include <bpf/btf.h>
> +#include "kmem_cache_iter.skel.h"
> +
> +static void test_kmem_cache_iter_check_task(struct kmem_cache_iter *skel)
> +{
> +	LIBBPF_OPTS(bpf_test_run_opts, opts,
> +		.flags = BPF_F_TEST_RUN_ON_CPU,
> +	);
> +	int prog_fd = bpf_program__fd(skel->progs.check_task_struct);
> +
> +	/* get task_struct and check it if's from a slab cache */
> +	bpf_prog_test_run_opts(prog_fd, &opts);
> +
> +	/* the BPF program should set 'found' variable */
> +	ASSERT_EQ(skel->bss->found, 1, "found task_struct");

Hmm.. I'm seeing a failure with found being -1, which means ...

> +}
> +
> +void test_kmem_cache_iter(void)
> +{
> +	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
> +	struct kmem_cache_iter *skel = NULL;
> +	union bpf_iter_link_info linfo = {};
> +	struct bpf_link *link;
> +	char buf[1024];
> +	int iter_fd;
> +
> +	skel = kmem_cache_iter__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "kmem_cache_iter__open_and_load"))
> +		return;
> +
> +	opts.link_info = &linfo;
> +	opts.link_info_len = sizeof(linfo);
> +
> +	link = bpf_program__attach_iter(skel->progs.slab_info_collector, &opts);
> +	if (!ASSERT_OK_PTR(link, "attach_iter"))
> +		goto destroy;
> +
> +	iter_fd = bpf_iter_create(bpf_link__fd(link));
> +	if (!ASSERT_GE(iter_fd, 0, "iter_create"))
> +		goto free_link;
> +
> +	memset(buf, 0, sizeof(buf));
> +	while (read(iter_fd, buf, sizeof(buf) > 0)) {
> +		/* read out all contents */
> +		printf("%s", buf);
> +	}
> +
> +	/* next reads should return 0 */
> +	ASSERT_EQ(read(iter_fd, buf, sizeof(buf)), 0, "read");
> +
> +	test_kmem_cache_iter_check_task(skel);
> +
> +	close(iter_fd);
> +
> +free_link:
> +	bpf_link__destroy(link);
> +destroy:
> +	kmem_cache_iter__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h
> index c41ee80533ca219a..3305dc3a74b32481 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter.h
> @@ -24,6 +24,7 @@
>  #define BTF_F_PTR_RAW BTF_F_PTR_RAW___not_used
>  #define BTF_F_ZERO BTF_F_ZERO___not_used
>  #define bpf_iter__ksym bpf_iter__ksym___not_used
> +#define bpf_iter__kmem_cache bpf_iter__kmem_cache___not_used
>  #include "vmlinux.h"
>  #undef bpf_iter_meta
>  #undef bpf_iter__bpf_map
> @@ -48,6 +49,7 @@
>  #undef BTF_F_PTR_RAW
>  #undef BTF_F_ZERO
>  #undef bpf_iter__ksym
> +#undef bpf_iter__kmem_cache
>  
>  struct bpf_iter_meta {
>  	struct seq_file *seq;
> @@ -165,3 +167,8 @@ struct bpf_iter__ksym {
>  	struct bpf_iter_meta *meta;
>  	struct kallsym_iter *ksym;
>  };
> +
> +struct bpf_iter__kmem_cache {
> +	struct bpf_iter_meta *meta;
> +	struct kmem_cache *s;
> +} __attribute__((preserve_access_index));
> diff --git a/tools/testing/selftests/bpf/progs/kmem_cache_iter.c b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> new file mode 100644
> index 0000000000000000..3f6ec15a1bf6344c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Google */
> +
> +#include "bpf_iter.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +#define SLAB_NAME_MAX  256
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(void *));
> +	__uint(value_size, SLAB_NAME_MAX);
> +	__uint(max_entries, 1024);
> +} slab_hash SEC(".maps");
> +
> +extern struct kmem_cache *bpf_get_kmem_cache(__u64 addr) __ksym;
> +
> +/* result, will be checked by userspace */
> +int found;
> +
> +SEC("iter/kmem_cache")
> +int slab_info_collector(struct bpf_iter__kmem_cache *ctx)
> +{
> +	struct seq_file *seq = ctx->meta->seq;
> +	struct kmem_cache *s = ctx->s;
> +
> +	if (s) {
> +		char name[SLAB_NAME_MAX];
> +
> +		/*
> +		 * To make sure if the slab_iter implements the seq interface
> +		 * properly and it's also useful for debugging.
> +		 */
> +		BPF_SEQ_PRINTF(seq, "%s: %u\n", s->name, s->object_size);
> +
> +		bpf_probe_read_kernel_str(name, sizeof(name), s->name);
> +		bpf_map_update_elem(&slab_hash, &s, name, BPF_NOEXIST);
> +	}
> +
> +	return 0;
> +}
> +
> +SEC("raw_tp/bpf_test_finish")
> +int BPF_PROG(check_task_struct)
> +{
> +	__u64 curr = bpf_get_current_task();
> +	struct kmem_cache *s;
> +	char *name;
> +
> +	s = bpf_get_kmem_cache(curr);
> +	if (s == NULL) {
> +		found = -1;
> +		return 0;

... it cannot find a kmem_cache for the current task.  This program is
run by bpf_prog_test_run_opts() with BPF_F_TEST_RUN_ON_CPU.  So I think
the curr should point a task_struct in a slab cache.

Am I missing something?

Thanks,
Namhyung

> +	}
> +
> +	name = bpf_map_lookup_elem(&slab_hash, &s);
> +	if (name && !bpf_strncmp(name, 11, "task_struct"))
> +		found = 1;
> +	else
> +		found = -2;
> +
> +	return 0;
> +}
> -- 
> 2.46.1.824.gd892dcdcdd-goog
>