diff mbox series

[bpf-next,v7,6/8] selftests/bpf: detach a struct_ops link from the subsystem managing it.

Message ID 20240530065946.979330-7-thinker.li@gmail.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series Notify user space when a struct_ops object is detached/unregistered | expand

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bpf/vmtest-bpf-next-PR success PR summary
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/apply fail Patch does not apply to bpf-next-0

Commit Message

Kui-Feng Lee May 30, 2024, 6:59 a.m. UTC 
From: Kui-Feng Lee <thinker.li@gmail.com>

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(+)

Comments

Martin KaFai Lau May 30, 2024, 11:02 p.m. UTC | #1 
On 5/29/24 11:59 PM, thinker.li@gmail.com wrote:
> From: Kui-Feng Lee <thinker.li@gmail.com>
> 
> 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;
>   }

[ ... ]

>   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();

A summary of the offline discussion with Kui-Feng.

* serial_ is currently unnecessary for the test_struct_ops_module. It was a 
leftover because of a negative test case that was removed in the later revision 
of the initial struct_ops kmod support.
* Better don't renew this currently unnecessary serial_ requirement.
* The link_to_detach should only be initialized for a particular test. This can 
be done by checking a poison value in the bpf_testmod_ops.
* The reg() should complain and error out if the link_to_detach has already been 
set.

Patch 6 and 7 needs to be a followup. Path 1-5 and 8 look good and are applied. 
Thanks.
diff mbox series

Patch

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 56b787a89876..3ce2f7c3815d 100644
--- a/tools/testing/selftests/bpf/progs/struct_ops_detach.c
+++ b/tools/testing/selftests/bpf/progs/struct_ops_detach.c
@@ -3,8 +3,15 @@ 
 #include <vmlinux.h>
 #include <bpf/bpf_helpers.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();
+}