[PATCH bpf-next v4 6/7] selftests/bpf: detach a struct_ops link from the subsystem managing it.

Kui-Feng Lee
2024-05-21T22:53:09Z

Not only a user space program can detach a struct_ops link, the subsystem
managing a link can also detach the link. This patch adds a kfunc to
simulate detaching a link by the subsystem managing it and makes sure user
space programs get notified through epoll.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 42 ++++++++++++
.../bpf/bpf_testmod/bpf_testmod_kfunc.h | 1 +
.../bpf/prog_tests/test_struct_ops_module.c | 67 +++++++++++++++++++
.../selftests/bpf/progs/struct_ops_detach.c | 7 ++
4 files changed, 117 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 0a09732cde4b..2b3a89609b7e 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -744,6 +744,38 @@ __bpf_kfunc int bpf_kfunc_call_kernel_getpeername(struct addr_args *args)
return err;
}

+static DEFINE_SPINLOCK(detach_lock);
+static struct bpf_link *link_to_detach;
+
+__bpf_kfunc int bpf_dummy_do_link_detach(void)
+{
+ struct bpf_link *link;
+ int ret = -ENOENT;
+
+ /* A subsystem must ensure that a link is valid when detaching the
+ * link. In order to achieve that, the subsystem may need to obtain
+ * a lock to safeguard a table that holds the pointer to the link
+ * being detached. However, the subsystem cannot invoke
+ * link->ops->detach() while holding the lock because other tasks
+ * may be in the process of unregistering, which could lead to
+ * acquiring the same lock and causing a deadlock. This is why
+ * bpf_link_inc_not_zero() is used to maintain the link's validity.
+ */
+ spin_lock(&detach_lock);
+ link = link_to_detach;
+ /* Make sure the link is still valid by increasing its refcnt */
+ if (link && IS_ERR(bpf_link_inc_not_zero(link)))
+ link = NULL;
+ spin_unlock(&detach_lock);
+
+ if (link) {
+ ret = link->ops->detach(link);
+ bpf_link_put(link);
+ }
+
+ return ret;
+}
+
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)
@@ -780,6 +812,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_kernel_sendmsg, KF_SLEEPABLE)
BTF_ID_FLAGS(func, bpf_kfunc_call_sock_sendmsg, KF_SLEEPABLE)
BTF_ID_FLAGS(func, bpf_kfunc_call_kernel_getsockname, KF_SLEEPABLE)
BTF_ID_FLAGS(func, bpf_kfunc_call_kernel_getpeername, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_dummy_do_link_detach)
BTF_KFUNCS_END(bpf_testmod_check_kfunc_ids)

static int bpf_testmod_ops_init(struct btf *btf)
@@ -832,11 +865,20 @@ static int bpf_dummy_reg(void *kdata, struct bpf_link *link)
if (ops->test_2)
ops->test_2(4, ops->data);

+ spin_lock(&detach_lock);
+ if (!link_to_detach)
+ link_to_detach = link;
+ spin_unlock(&detach_lock);
+
return 0;
}

static void bpf_dummy_unreg(void *kdata, struct bpf_link *link)
{
+ spin_lock(&detach_lock);
+ if (link == link_to_detach)
+ link_to_detach = NULL;
+ spin_unlock(&detach_lock);
}

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 b0d586a6751f..19131baf4a9e 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
@@ -121,6 +121,7 @@ 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;

void bpf_kfunc_common_test(void) __ksym;

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 bbcf12696a6b..f4000bf04752 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
@@ -2,6 +2,7 @@
/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
#include <test_progs.h>
#include <time.h>
+#include <network_helpers.h>

#include <sys/epoll.h>

@@ -297,6 +298,70 @@ static void test_detach_link(void)
struct_ops_detach__destroy(skel);
}

+/* Detach a link from the subsystem that the link was registered to */
+static void test_subsystem_detach(void)
+{
+ LIBBPF_OPTS(bpf_test_run_opts, topts,
+ .data_in = &pkt_v4,
+ .data_size_in = sizeof(pkt_v4));
+ struct epoll_event ev, events[2];
+ struct struct_ops_detach *skel;
+ struct bpf_link *link = NULL;
+ int fd, epollfd = -1, nfds;
+ int prog_fd;
+ 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;
+
+ prog_fd = bpf_program__fd(skel->progs.start_detach);
+ if (!ASSERT_GE(prog_fd, 0, "start_detach_fd"))
+ goto cleanup;
+
+ /* Do detachment from the registered subsystem */
+ err = bpf_prog_test_run_opts(prog_fd, &topts);
+ if (!ASSERT_OK(err, "start_detach_run"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(topts.retval, 0, "start_detach_run_retval"))
+ 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;
+
+ /* Wait for EPOLLHUP */
+ nfds = epoll_wait(epollfd, events, 2, 5000);
+ 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:
+ if (epollfd >= 0)
+ close(epollfd);
+ bpf_link__destroy(link);
+ struct_ops_detach__destroy(skel);
+}
+
void serial_test_struct_ops_module(void)
{
if (test__start_subtest("struct_ops_load"))
@@ -311,5 +376,7 @@ void serial_test_struct_ops_module(void)
test_struct_ops_forgotten_cb();
if (test__start_subtest("test_detach_link"))
test_detach_link();
+ if (test__start_subtest("test_subsystem_detach"))
+ test_subsystem_detach();
}

diff --git a/tools/testing/selftests/bpf/progs/struct_ops_detach.c b/tools/testing/selftests/bpf/progs/struct_ops_detach.c
index 45eacc2ca657..5c742b0df04d 100644
--- a/tools/testing/selftests/bpf/progs/struct_ops_detach.c
+++ b/tools/testing/selftests/bpf/progs/struct_ops_detach.c
@@ -2,8 +2,15 @@
/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
#include <vmlinux.h>
#include "../bpf_testmod/bpf_testmod.h"
+#include "../bpf_testmod/bpf_testmod_kfunc.h"

char _license[] SEC("license") = "GPL";

SEC(".struct_ops.link")
struct bpf_testmod_ops testmod_do_detach;
+
+SEC("tc")
+int start_detach(void *skb)
+{
+ return bpf_dummy_do_link_detach();
+}
--
2.34.1