Re: [PATCH bpf-next 2/2] selftests/bpf: Add a test for open coded kmem_cache iter

[Namhyung Kim <namhyung@kernel.org>]

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@kernel.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