bpf: Remove bpf_cpumask_kptr_get() kfunc

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 (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, as well as its selftests and
documentation.

Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230316054028.88924-5-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index 98eea62..db9da21 100644 (file)
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -82,34 +82,6 @@ __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;
@@ -435,7 +407,6 @@ 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 6c0fe23..cdf4acc 100644 (file)
--- 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 7623782..0c5b785 100644 (file)
--- 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 9f726d5..db4f94e 100644 (file)
--- a/tools/testing/selftests/bpf/progs/cpumask_failure.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c
@@ -95,30 +95,6 @@ int BPF_PROG(test_insert_remove_no_release, struct task_struct *task, u64 clone_
 }
 
 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 fe928ff..2fcdd7f 100644 (file)
--- a/tools/testing/selftests/bpf/progs/cpumask_success.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_success.c
@@ -395,36 +395,6 @@ int BPF_PROG(test_insert_remove_release, struct task_struct *task, u64 clone_fla
 }
 
 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)
 {
        struct bpf_cpumask *local, *prev;