From: Namhyung Kim <namhyung@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
bpf <bpf@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Vlastimil Babka <vbabka@suse.cz>,
Roman Gushchin <roman.gushchin@linux.dev>,
Hyeonggon Yoo <42.hyeyoo@gmail.com>,
linux-mm <linux-mm@kvack.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Kees Cook <kees@kernel.org>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests/bpf: Add a test for open coded kmem_cache iter
Date: Tue, 29 Oct 2024 18:40:46 -0700 [thread overview]
Message-ID: <ZyGOng76IBUs8PtY@google.com> (raw)
In-Reply-To: <CAADnVQLA=QE9HwH+9tA+G8uppXK0-yk-hbiBHaOmjkjVENYCsA@mail.gmail.com>
Hello,
On Thu, Oct 24, 2024 at 11:08:00AM -0700, Alexei Starovoitov wrote:
> On Thu, Oct 24, 2024 at 12:48 AM Namhyung Kim <namhyung@kernel.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@kernel.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.
Sure, will update in v3.
>
> > +
> > + 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.
I don't think so. The last element should be an actual slab cache and
then the iterator will return NULL to break the loop. I don't expect it
will hit the if statement.
Thanks,
Namhyung
next prev parent reply other threads:[~2024-10-30 1:40 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-24 7:48 [PATCH v2 bpf-next 1/2] bpf: Add open coded version of kmem_cache iterator Namhyung Kim
2024-10-24 7:48 ` [PATCH v2 bpf-next 2/2] selftests/bpf: Add a test for open coded kmem_cache iter Namhyung Kim
2024-10-24 18:08 ` Alexei Starovoitov
2024-10-30 1:40 ` Namhyung Kim [this message]
2024-10-30 21:35 ` Namhyung Kim
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