[PATCH bpf-next 4/5] bpf: Remove bpf_cpumask_kptr_get() kfunc

David Vernet
2023-03-16T01:41:47Z

Now that struct bpf_cpumask is RCU safe, there's no need for this kfunc.
Rather than doing the following:

private(MASK) static struct bpf_cpumask __kptr *global;

int BPF_PROG(prog, s32 cpu, ...)
{
struct bpf_cpumask *cpumask;

bpf_rcu_read_lock();
cpumask = bpf_cpumask_kptr_get(&global);
if (!cpumask) {
bpf_rcu_read_unlock();
return -1;
}
bpf_cpumask_setall(cpumask);
...
bpf_cpumask_release(cpumask);
bpf_rcu_read_unlock();
}

Programs can instead simply do this (assume same global cpumask):

int BPF_PROG(prog, ...)
{
struct bpf_cpumask *cpumask;

bpf_rcu_read_lock();
cpumask = global;
if (!cpumask) {
bpf_rcu_read_unlock();
return -1;
}
bpf_cpumask_setall(cpumask);
...
bpf_rcu_read_unlock();
}

In other words, no extra atomic acquire / release, and less boilerplate
code.

This patch removes both the kfunc, and its selftests. A subsequent patch
will update the BPF documentation to use the new method for accessing
cpumasks with RCU protection.

Signed-off-by: David Vernet <void@manifault.com>
---
kernel/bpf/cpumask.c | 29 ------------------
.../selftests/bpf/prog_tests/cpumask.c | 1 -
.../selftests/bpf/progs/cpumask_common.h | 1 -
.../selftests/bpf/progs/cpumask_failure.c | 24 ---------------
.../selftests/bpf/progs/cpumask_success.c | 30 -------------------
5 files changed, 85 deletions(-)

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index 9ab462c5848a..5329d07114e9 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -81,34 +81,6 @@ __bpf_kfunc struct bpf_cpumask *bpf_cpumask_acquire(struct bpf_cpumask *cpumask)
return cpumask;
}

-/**
- * bpf_cpumask_kptr_get() - Attempt to acquire a reference to a BPF cpumask
- * stored in a map.
- * @cpumaskp: A pointer to a BPF cpumask map value.
- *
- * Attempts to acquire a reference to a BPF cpumask stored in a map value. The
- * cpumask returned by this function must either be embedded in a map as a
- * kptr, or freed with bpf_cpumask_release(). This function may return NULL if
- * no BPF cpumask was found in the specified map value.
- */
-__bpf_kfunc struct bpf_cpumask *bpf_cpumask_kptr_get(struct bpf_cpumask **cpumaskp)
-{
- struct bpf_cpumask *cpumask;
-
- /* The BPF memory allocator frees memory backing its caches in an RCU
- * callback. Thus, we can safely use RCU to ensure that the cpumask is
- * safe to read.
- */
- rcu_read_lock();
-
- cpumask = READ_ONCE(*cpumaskp);
- if (cpumask && !refcount_inc_not_zero(&cpumask->usage))
- cpumask = NULL;
-
- rcu_read_unlock();
- return cpumask;
-}
-
static void cpumask_free_cb(struct rcu_head *head)
{
struct bpf_cpumask *cpumask;
@@ -434,7 +406,6 @@ BTF_SET8_START(cpumask_kfunc_btf_ids)
BTF_ID_FLAGS(func, bpf_cpumask_create, KF_ACQUIRE | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cpumask_release, KF_RELEASE | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_cpumask_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
-BTF_ID_FLAGS(func, bpf_cpumask_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cpumask_first, KF_RCU)
BTF_ID_FLAGS(func, bpf_cpumask_first_zero, KF_RCU)
BTF_ID_FLAGS(func, bpf_cpumask_set_cpu, KF_RCU)
diff --git a/tools/testing/selftests/bpf/prog_tests/cpumask.c b/tools/testing/selftests/bpf/prog_tests/cpumask.c
index 6c0fe23498c7..cdf4acc18e4c 100644
--- a/tools/testing/selftests/bpf/prog_tests/cpumask.c
+++ b/tools/testing/selftests/bpf/prog_tests/cpumask.c
@@ -16,7 +16,6 @@ static const char * const cpumask_success_testcases[] = {
"test_copy_any_anyand",
"test_insert_leave",
"test_insert_remove_release",
- "test_insert_kptr_get_release",
"test_global_mask_rcu",
};

diff --git a/tools/testing/selftests/bpf/progs/cpumask_common.h b/tools/testing/selftests/bpf/progs/cpumask_common.h
index 7623782fbd62..0c5b785a93e4 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_common.h
+++ b/tools/testing/selftests/bpf/progs/cpumask_common.h
@@ -26,7 +26,6 @@ struct array_map {
struct bpf_cpumask *bpf_cpumask_create(void) __ksym;
void bpf_cpumask_release(struct bpf_cpumask *cpumask) __ksym;
struct bpf_cpumask *bpf_cpumask_acquire(struct bpf_cpumask *cpumask) __ksym;
-struct bpf_cpumask *bpf_cpumask_kptr_get(struct bpf_cpumask **cpumask) __ksym;
u32 bpf_cpumask_first(const struct cpumask *cpumask) __ksym;
u32 bpf_cpumask_first_zero(const struct cpumask *cpumask) __ksym;
void bpf_cpumask_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
diff --git a/tools/testing/selftests/bpf/progs/cpumask_failure.c b/tools/testing/selftests/bpf/progs/cpumask_failure.c
index 9f726d55f747..db4f94e72b61 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_failure.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c
@@ -94,30 +94,6 @@ int BPF_PROG(test_insert_remove_no_release, struct task_struct *task, u64 clone_
return 0;
}

-SEC("tp_btf/task_newtask")
-__failure __msg("Unreleased reference")
-int BPF_PROG(test_kptr_get_no_release, struct task_struct *task, u64 clone_flags)
-{
- struct bpf_cpumask *cpumask;
- struct __cpumask_map_value *v;
-
- cpumask = create_cpumask();
- if (!cpumask)
- return 0;
-
- if (cpumask_map_insert(cpumask))
- return 0;
-
- v = cpumask_map_value_lookup();
- if (!v)
- return 0;
-
- cpumask = bpf_cpumask_kptr_get(&v->cpumask);
-
- /* cpumask is never released. */
- return 0;
-}
-
SEC("tp_btf/task_newtask")
__failure __msg("NULL pointer passed to trusted arg0")
int BPF_PROG(test_cpumask_null, struct task_struct *task, u64 clone_flags)
diff --git a/tools/testing/selftests/bpf/progs/cpumask_success.c b/tools/testing/selftests/bpf/progs/cpumask_success.c
index fe928ff72a06..2fcdd7f68ac7 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_success.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_success.c
@@ -394,36 +394,6 @@ int BPF_PROG(test_insert_remove_release, struct task_struct *task, u64 clone_fla
return 0;
}

-SEC("tp_btf/task_newtask")
-int BPF_PROG(test_insert_kptr_get_release, struct task_struct *task, u64 clone_flags)
-{
- struct bpf_cpumask *cpumask;
- struct __cpumask_map_value *v;
-
- cpumask = create_cpumask();
- if (!cpumask)
- return 0;
-
- if (cpumask_map_insert(cpumask)) {
- err = 3;
- return 0;
- }
-
- v = cpumask_map_value_lookup();
- if (!v) {
- err = 4;
- return 0;
- }
-
- cpumask = bpf_cpumask_kptr_get(&v->cpumask);
- if (cpumask)
- bpf_cpumask_release(cpumask);
- else
- err = 5;
-
- return 0;
-}
-
SEC("tp_btf/task_newtask")
int BPF_PROG(test_global_mask_rcu, struct task_struct *task, u64 clone_flags)
{
--
2.39.0