Re: [PATCH bpf-next v2 4/6] selftests/bpf: test struct_ops with epoll

[Martin KaFai Lau <martin.lau@linux.dev>]

On 5/6/24 10:55 PM, Kui-Feng Lee wrote:
> Verify whether a user space program is informed through epoll with EPOLLHUP
> when a struct_ops object is detached.
> 
> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
> ---
>   .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 13 +++++
>   .../bpf/bpf_testmod/bpf_testmod_kfunc.h       |  1 +
>   .../bpf/prog_tests/test_struct_ops_module.c   | 57 +++++++++++++++++++
>   .../selftests/bpf/progs/struct_ops_detach.c   | 31 ++++++++++
>   4 files changed, 102 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_detach.c
> 
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index e24a18bfee14..c89a6414c69f 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -10,6 +10,7 @@
>   #include <linux/percpu-defs.h>
>   #include <linux/sysfs.h>
>   #include <linux/tracepoint.h>
> +#include <linux/workqueue.h>
>   #include "bpf_testmod.h"
>   #include "bpf_testmod_kfunc.h"
>   
> @@ -498,6 +499,9 @@ __bpf_kfunc void bpf_kfunc_call_test_sleepable(void)
>   {
>   }
>   
> +static DEFINE_MUTEX(detach_mutex);
> +static struct bpf_link *link_to_detach;
> +
>   BTF_KFUNCS_START(bpf_testmod_check_kfunc_ids)
>   BTF_ID_FLAGS(func, bpf_testmod_test_mod_kfunc)
>   BTF_ID_FLAGS(func, bpf_kfunc_call_test1)
> @@ -577,11 +581,20 @@ static int bpf_dummy_reg(void *kdata, struct bpf_link *link)
>   	if (ops->test_2)
>   		ops->test_2(4, ops->data);
>   
> +	mutex_lock(&detach_mutex);
> +	if (!link_to_detach)
> +		link_to_detach = link;
> +	mutex_unlock(&detach_mutex);
> +
>   	return 0;
>   }
>   
>   static void bpf_dummy_unreg(void *kdata, struct bpf_link *link)
>   {
> +	mutex_lock(&detach_mutex);
> +	if (link == link_to_detach)
> +		link_to_detach = NULL;
> +	mutex_unlock(&detach_mutex);

The reg/unreg changes should belong to the next patch.

>   }
>   
>   static int bpf_testmod_test_1(void)
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
> index ce5cd763561c..9f9b60880fd3 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
> @@ -105,6 +105,7 @@ void bpf_kfunc_call_test_fail1(struct prog_test_fail1 *p);
>   void bpf_kfunc_call_test_fail2(struct prog_test_fail2 *p);
>   void bpf_kfunc_call_test_fail3(struct prog_test_fail3 *p);
>   void bpf_kfunc_call_test_mem_len_fail1(void *mem, int len);
> +int bpf_dummy_do_link_detach(void) __ksym;

The kfunc is not added in this patch either.

>   
>   void bpf_kfunc_common_test(void) __ksym;
>   #endif /* _BPF_TESTMOD_KFUNC_H */
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
> index bd39586abd5a..f39455b81664 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
> @@ -2,8 +2,12 @@
>   /* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
>   #include <test_progs.h>
>   #include <time.h>
> +#include <network_helpers.h>

What is needed from network_herlpers.h?

> +
> +#include <sys/epoll.h>
>   
>   #include "struct_ops_module.skel.h"
> +#include "struct_ops_detach.skel.h"
>   
>   static void check_map_info(struct bpf_map_info *info)
>   {
> @@ -174,6 +178,57 @@ static void test_struct_ops_incompatible(void)
>   	struct_ops_module__destroy(skel);
>   }
>   
> +/* Detach a link from a user space program */
> +static void test_detach_link(void)
> +{
> +	struct epoll_event ev, events[2];
> +	struct struct_ops_detach *skel;
> +	struct bpf_link *link = NULL;
> +	int fd, epollfd = -1, nfds;
> +	int err;
> +
> +	skel = struct_ops_detach__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "struct_ops_detach__open_and_load"))
> +		return;
> +
> +	link = bpf_map__attach_struct_ops(skel->maps.testmod_do_detach);
> +	if (!ASSERT_OK_PTR(link, "attach_struct_ops"))
> +		goto cleanup;
> +
> +	fd = bpf_link__fd(link);
> +	if (!ASSERT_GE(fd, 0, "link_fd"))
> +		goto cleanup;
> +
> +	epollfd = epoll_create1(0);
> +	if (!ASSERT_GE(epollfd, 0, "epoll_create1"))
> +		goto cleanup;
> +
> +	ev.events = EPOLLHUP;
> +	ev.data.fd = fd;
> +	err = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev);
> +	if (!ASSERT_OK(err, "epoll_ctl"))
> +		goto cleanup;
> +
> +	err = bpf_link__detach(link);
> +	if (!ASSERT_OK(err, "detach_link"))
> +		goto cleanup;
> +
> +	/* Wait for EPOLLHUP */
> +	nfds = epoll_wait(epollfd, events, 2, 500);
> +	if (!ASSERT_EQ(nfds, 1, "epoll_wait"))
> +		goto cleanup;
> +
> +	if (!ASSERT_EQ(events[0].data.fd, fd, "epoll_wait_fd"))
> +		goto cleanup;
> +	if (!ASSERT_TRUE(events[0].events & EPOLLHUP, "events[0].events"))
> +		goto cleanup;
> +
> +cleanup:
> +	close(epollfd);

Better check epollfd since it is init to -1. There are cases that epollfd is -1 
here.

> +	bpf_link__destroy(link);
> +	struct_ops_detach__destroy(skel);
> +}
> +
>   void serial_test_struct_ops_module(void)
>   {
>   	if (test__start_subtest("test_struct_ops_load"))
> @@ -182,5 +237,7 @@ void serial_test_struct_ops_module(void)
>   		test_struct_ops_not_zeroed();
>   	if (test__start_subtest("test_struct_ops_incompatible"))
>   		test_struct_ops_incompatible();
> +	if (test__start_subtest("test_detach_link"))
> +		test_detach_link();
>   }
>   
> diff --git a/tools/testing/selftests/bpf/progs/struct_ops_detach.c b/tools/testing/selftests/bpf/progs/struct_ops_detach.c
> new file mode 100644
> index 000000000000..aeb355b3bea3
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/struct_ops_detach.c
> @@ -0,0 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include "../bpf_testmod/bpf_testmod.h"
> +#include "../bpf_testmod/bpf_testmod_kfunc.h"

The _kfunc.h should not be needed in this patch either.

> +
> +char _license[] SEC("license") = "GPL";
> +
> +int test_1_result = 0;
> +int test_2_result = 0;

Are these global vars tested? If not, can the test_1 and test_2 programs be 
removed? or some of them is not optional?

> +
> +SEC("struct_ops/test_1")
> +int BPF_PROG(test_1)
> +{
> +	test_1_result = 0xdeadbeef;
> +	return 0;
> +}
> +
> +SEC("struct_ops/test_2")
> +void BPF_PROG(test_2, int a, int b)
> +{
> +	test_2_result = a + b;
> +}
> +
> +SEC(".struct_ops.link")
> +struct bpf_testmod_ops testmod_do_detach = {
> +	.test_1 = (void *)test_1,
> +	.test_2 = (void *)test_2,
> +};