netdev - Re: [PATCH bpf-next 4/4] selftests/bpf: add auto-detach test

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Date:   Wed, 22 May 2019 23:19:59 +0000
From:   Roman Gushchin <guro@...com>
To:     Stanislav Fomichev <sdf@...ichev.me>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Kernel Team <Kernel-team@...com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 4/4] selftests/bpf: add auto-detach test

On Wed, May 22, 2019 at 03:24:38PM -0700, Stanislav Fomichev wrote:
> On 05/22, Roman Gushchin wrote:
> > Add a kselftest to cover bpf auto-detachment functionality.
> > The test creates a cgroup, associates some resources with it,
> > attaches a couple of bpf programs and deletes the cgroup.
> > 
> > Then it checks that bpf programs are going away in 5 seconds.
> > 
> > Expected output:
> >   $ ./test_cgroup_attach
> >   #override:PASS
> >   #multi:PASS
> >   #autodetach:PASS
> >   test_cgroup_attach:PASS
> > 
> > On a kernel without auto-detaching:
> >   $ ./test_cgroup_attach
> >   #override:PASS
> >   #multi:PASS
> >   #autodetach:FAIL
> >   test_cgroup_attach:FAIL
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> > ---
> >  .../selftests/bpf/test_cgroup_attach.c        | 108 +++++++++++++++++-
> >  1 file changed, 107 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/testing/selftests/bpf/test_cgroup_attach.c b/tools/testing/selftests/bpf/test_cgroup_attach.c
> > index 93d4fe295e7d..36441fd0f392 100644
> > --- a/tools/testing/selftests/bpf/test_cgroup_attach.c
> > +++ b/tools/testing/selftests/bpf/test_cgroup_attach.c
> > @@ -456,9 +456,115 @@ static int test_multiprog(void)
> >  	return rc;
> >  }
> >  
> > +static int test_autodetach(void)
> > +{
> > +	__u32 prog_cnt = 4, attach_flags;
> > +	int allow_prog[2] = {0};
> > +	__u32 prog_ids[2] = {0};
> > +	int cg = 0, i, rc = -1;
> > +	void *ptr = NULL;
> > +	int attempts;
> > +
> > +
> > +	for (i = 0; i < ARRAY_SIZE(allow_prog); i++) {
> > +		allow_prog[i] = prog_load_cnt(1, 1 << i);
> > +		if (!allow_prog[i])
> > +			goto err;
> > +	}
> > +
> > +	if (setup_cgroup_environment())
> > +		goto err;
> > +
> > +	/* create a cgroup, attach two programs and remember their ids */
> > +	cg = create_and_get_cgroup("/cg_autodetach");
> > +	if (cg < 0)
> > +		goto err;
> > +
> > +	if (join_cgroup("/cg_autodetach"))
> > +		goto err;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(allow_prog); i++) {
> > +		if (bpf_prog_attach(allow_prog[i], cg, BPF_CGROUP_INET_EGRESS,
> > +				    BPF_F_ALLOW_MULTI)) {
> > +			log_err("Attaching prog[%d] to cg:egress", i);
> > +			goto err;
> > +		}
> > +	}
> > +
> > +	/* make sure that programs are attached and run some traffic */
> > +	assert(bpf_prog_query(cg, BPF_CGROUP_INET_EGRESS, 0, &attach_flags,
> > +			      prog_ids, &prog_cnt) == 0);
> > +	assert(system(PING_CMD) == 0);
> > +
> > +	/* allocate some memory (4Mb) to pin the original cgroup */
> > +	ptr = malloc(4 * (1 << 20));
> > +	if (!ptr)
> > +		goto err;
> > +
> > +	/* close programs and cgroup fd */
> > +	for (i = 0; i < ARRAY_SIZE(allow_prog); i++) {
> > +		close(allow_prog[i]);
> > +		allow_prog[i] = 0;
> > +	}
> > +
> > +	close(cg);
> > +	cg = 0;
> > +
> > +	/* leave the cgroup and remove it. don't detach programs */
> > +	cleanup_cgroup_environment();
> > +
> 
> [..]
> > +	/* programs must stay pinned by the allocated memory */
> > +	for (i = 0; i < ARRAY_SIZE(prog_ids); i++) {
> > +		int fd = bpf_prog_get_fd_by_id(prog_ids[i]);
> > +
> > +		if (fd < 0)
> > +			goto err;
> > +		close(fd);
> > +	}
> This looks a bit flaky. It's essentially the same check you later
> do in a for loop. I guess there is a chance that async auto-detach
> might happen right after cleanup_cgroup_environment and before this for loop?

Ah, this section remained from an earlier version which had another step.
I'll remove it completely, it's totally useless now.

Thanks!