On 5/29/24 11:59 PM, thinker.li@xxxxxxxxx wrote:
From: Kui-Feng Lee <thinker.li@xxxxxxxxx>
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@xxxxxxxxx>
---
.../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.
