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Message-ID: <7b19ad7f-163b-44ed-bc70-f973a7a6f303@linux.dev>
Date: Fri, 18 Oct 2024 11:46:31 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
bpf@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <roman.gushchin@...ux.dev>,
Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
Arnaldo Carvalho de Melo <acme@...nel.org>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Add a test for open coded
kmem_cache iter
On 10/17/24 1:06 AM, Namhyung Kim wrote:
> The new subtest is attached to sleepable fentry of syncfs() syscall.
> It iterates the kmem_cache using bpf_for_each loop and count the number
> of entries. Finally it checks it with the number of entries from the
> regular iterator.
>
> $ ./vmtest.sh -- ./test_progs -t kmem_cache_iter
> ...
> #130/1 kmem_cache_iter/check_task_struct:OK
> #130/2 kmem_cache_iter/check_slabinfo:OK
> #130/3 kmem_cache_iter/open_coded_iter:OK
> #130 kmem_cache_iter:OK
> Summary: 1/3 PASSED, 0 SKIPPED, 0 FAILED
>
> Also simplify the code by using attach routine of the skeleton.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> .../testing/selftests/bpf/bpf_experimental.h | 6 ++++
> .../bpf/prog_tests/kmem_cache_iter.c | 28 +++++++++++--------
> .../selftests/bpf/progs/kmem_cache_iter.c | 24 ++++++++++++++++
> 3 files changed, 46 insertions(+), 12 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> index b0668f29f7b394eb..cd8ecd39c3f3c68d 100644
> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> @@ -582,4 +582,10 @@ extern int bpf_wq_set_callback_impl(struct bpf_wq *wq,
> unsigned int flags__k, void *aux__ign) __ksym;
> #define bpf_wq_set_callback(timer, cb, flags) \
> bpf_wq_set_callback_impl(timer, cb, flags, NULL)
> +
> +struct bpf_iter_kmem_cache;
> +extern int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) __weak __ksym;
> +extern struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) __weak __ksym;
> +extern void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) __weak __ksym;
> +
> #endif
> diff --git a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> index 848d8fc9171fae45..a1fd3bc57c0b21bb 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> @@ -68,12 +68,18 @@ static void subtest_kmem_cache_iter_check_slabinfo(struct kmem_cache_iter *skel)
> fclose(fp);
> }
>
> +static void subtest_kmem_cache_iter_open_coded(struct kmem_cache_iter *skel)
> +{
> + /* To trigger the open coded iterator attached to the syscall */
> + syncfs(0);
> +
> + /* It should be same as we've seen from the explicit iterator */
> + ASSERT_EQ(skel->bss->open_coded_seen, skel->bss->kmem_cache_seen, "open_code_seen_eq");
> +}
> +
> 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[256];
> int iter_fd;
>
> @@ -81,16 +87,12 @@ void test_kmem_cache_iter(void)
> 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"))
> + if (!ASSERT_OK(kmem_cache_iter__attach(skel), "skel_attach"))
with this change.
> goto destroy;
>
> - iter_fd = bpf_iter_create(bpf_link__fd(link));
> + iter_fd = bpf_iter_create(bpf_link__fd(skel->links.slab_info_collector));
> if (!ASSERT_GE(iter_fd, 0, "iter_create"))
> - goto free_link;
> + goto detach;
>
> memset(buf, 0, sizeof(buf));
> while (read(iter_fd, buf, sizeof(buf) > 0)) {
> @@ -105,11 +107,13 @@ void test_kmem_cache_iter(void)
> subtest_kmem_cache_iter_check_task_struct(skel);
> if (test__start_subtest("check_slabinfo"))
> subtest_kmem_cache_iter_check_slabinfo(skel);
> + if (test__start_subtest("open_coded_iter"))
> + subtest_kmem_cache_iter_open_coded(skel);
>
> close(iter_fd);
>
> -free_link:
> - bpf_link__destroy(link);
> +detach:
> + kmem_cache_iter__detach(skel);
nit. I think the kmem_cache_iter__destroy() below will also detach, so no need
to explicit kmem_cache_iter__detach().
> destroy:
> kmem_cache_iter__destroy(skel);
> }
> diff --git a/tools/testing/selftests/bpf/progs/kmem_cache_iter.c b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> index 72c9dafecd98406b..4c44aa279a5328fe 100644
> --- a/tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> +++ b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c
> @@ -2,6 +2,8 @@
> /* Copyright (c) 2024 Google */
>
> #include "bpf_iter.h"
> +#include "bpf_experimental.h"
> +#include "bpf_misc.h"
> #include <bpf/bpf_helpers.h>
> #include <bpf/bpf_tracing.h>
>
> @@ -33,6 +35,7 @@ extern struct kmem_cache *bpf_get_kmem_cache(u64 addr) __ksym;
> /* Result, will be checked by userspace */
> int task_struct_found;
> int kmem_cache_seen;
> +int open_coded_seen;
>
> SEC("iter/kmem_cache")
> int slab_info_collector(struct bpf_iter__kmem_cache *ctx)
> @@ -85,3 +88,24 @@ int BPF_PROG(check_task_struct)
> task_struct_found = -2;
> return 0;
> }
> +
> +SEC("fentry.s/" SYS_PREFIX "sys_syncfs")
> +int open_coded_iter(const void *ctx)
> +{
> + struct kmem_cache *s;
> +
> + bpf_for_each(kmem_cache, s) {
> + struct kmem_cache_result *r;
> + int idx = open_coded_seen;
> +
> + r = bpf_map_lookup_elem(&slab_result, &idx);
> + if (r == NULL)
> + break;
> +
> + open_coded_seen++;
I am not sure if this will work well if the testing system somehow has another
process calling syncfs. It is probably a good idea to guard this by checking the
tid of the test_progs at the beginning of this bpf prog.
> +
> + if (r->obj_size != s->size)
> + break;
> + }
> + return 0;
> +}
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