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Message-ID: <ZxfmKqEebyS4gryd@google.com>
Date: Tue, 22 Oct 2024 10:51:38 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Martin KaFai Lau <martin.lau@...ux.dev>
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 Fri, Oct 18, 2024 at 11:46:31AM -0700, Martin KaFai Lau wrote:
> 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().
Ok, will remove.
>
> > 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.
Right, I'll add the tid check.
Thanks for the review,
Namhyung
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