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Message-ID: <CAADnVQLA=QE9HwH+9tA+G8uppXK0-yk-hbiBHaOmjkjVENYCsA@mail.gmail.com>
Date: Thu, 24 Oct 2024 11:08:00 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	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 <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 <linux-mm@...ck.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests/bpf: Add a test for open coded
 kmem_cache iter

On Thu, Oct 24, 2024 at 12:48 AM Namhyung Kim <namhyung@...nel.org> 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>
> ---
> v2)
>  * remove unnecessary detach  (Martin)
>  * check pid in syncfs to prevent surprise  (Martin)
>  * remove unnecessary local variable  (Andrii)
>
>  .../testing/selftests/bpf/bpf_experimental.h  |  6 ++++
>  .../bpf/prog_tests/kmem_cache_iter.c          | 28 +++++++++++--------
>  .../selftests/bpf/progs/kmem_cache_iter.c     | 28 +++++++++++++++++++
>  3 files changed, 50 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..778b55bc1f912b98 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 +68,20 @@ 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)
> +{
> +       skel->bss->tgid = getpid();
> +
> +       /* 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 +89,12 @@ 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"))
>                 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 destroy;
>
>         memset(buf, 0, sizeof(buf));
>         while (read(iter_fd, buf, sizeof(buf) > 0)) {
> @@ -105,11 +109,11 @@ 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);
>  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..e62807caa7593604 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>
>
> @@ -30,9 +32,12 @@ struct {
>
>  extern struct kmem_cache *bpf_get_kmem_cache(u64 addr) __ksym;
>
> +unsigned int tgid;
> +
>  /* 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 +90,26 @@ 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;
> +
> +       if (tgid != bpf_get_current_pid_tgid() >> 32)
> +               return 0;

Pls use syscall prog type and prog_run() it.
No need to attach to exotic syscalls and filter by pid.

> +
> +       bpf_for_each(kmem_cache, s) {
> +               struct kmem_cache_result *r;
> +
> +               r = bpf_map_lookup_elem(&slab_result, &open_coded_seen);
> +               if (!r)
> +                       break;
> +
> +               open_coded_seen++;
> +
> +               if (r->obj_size != s->size)
> +                       break;

The order of 'if' and ++ should probably be changed ?
Otherwise the last object isn't sufficiently checked.

pw-bot: cr

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