bpf: Remove bpf_cgroup_kptr_get() kfunc

Now that bpf_cgroup_acquire() is KF_RCU | KF_RET_NULL,
bpf_cgroup_kptr_get() is redundant. Let's remove it, and update
selftests to instead use bpf_cgroup_acquire() where appropriate. The
next patch will update the BPF documentation to not mention
bpf_cgroup_kptr_get().

Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230411041633.179404-2-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 14 insertions, 67 deletions

diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
index b0e279f4652b..22914a70db54 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
@@ -21,10 +21,11 @@ struct hash_map {
 } __cgrps_kfunc_map SEC(".maps");
 
 struct cgroup *bpf_cgroup_acquire(struct cgroup *p) __ksym;
-struct cgroup *bpf_cgroup_kptr_get(struct cgroup **pp) __ksym;
 void bpf_cgroup_release(struct cgroup *p) __ksym;
 struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
 struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
 
 static inline struct __cgrps_kfunc_map_value *cgrps_kfunc_map_value_lookup(struct cgroup *cgrp)
 {
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
index 49347f12de39..0fa564a5cc5b 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
@@ -134,59 +134,6 @@ int BPF_PROG(cgrp_kfunc_acquire_unreleased, struct cgroup *cgrp, const char *pat
 }
 
 SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_non_kptr_param, struct cgroup *cgrp, const char *path)
-{
-	struct cgroup *kptr;
-
-	/* Cannot use bpf_cgroup_kptr_get() on a non-kptr, even on a valid cgroup. */
-	kptr = bpf_cgroup_kptr_get(&cgrp);
-	if (!kptr)
-		return 0;
-
-	bpf_cgroup_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_non_kptr_acquired, struct cgroup *cgrp, const char *path)
-{
-	struct cgroup *kptr, *acquired;
-
-	acquired = bpf_cgroup_acquire(cgrp);
-	if (!acquired)
-		return 0;
-
-	/* Cannot use bpf_cgroup_kptr_get() on a non-map-value, even if the kptr was acquired. */
-	kptr = bpf_cgroup_kptr_get(&acquired);
-	bpf_cgroup_release(acquired);
-	if (!kptr)
-		return 0;
-
-	bpf_cgroup_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_null, struct cgroup *cgrp, const char *path)
-{
-	struct cgroup *kptr;
-
-	/* Cannot use bpf_cgroup_kptr_get() on a NULL pointer. */
-	kptr = bpf_cgroup_kptr_get(NULL);
-	if (!kptr)
-		return 0;
-
-	bpf_cgroup_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/cgroup_mkdir")
 __failure __msg("Unreleased reference")
 int BPF_PROG(cgrp_kfunc_xchg_unreleased, struct cgroup *cgrp, const char *path)
 {
@@ -207,8 +154,8 @@ int BPF_PROG(cgrp_kfunc_xchg_unreleased, struct cgroup *cgrp, const char *path)
 }
 
 SEC("tp_btf/cgroup_mkdir")
-__failure __msg("Unreleased reference")
-int BPF_PROG(cgrp_kfunc_get_unreleased, struct cgroup *cgrp, const char *path)
+__failure __msg("must be referenced or trusted")
+int BPF_PROG(cgrp_kfunc_rcu_get_release, struct cgroup *cgrp, const char *path)
 {
 	struct cgroup *kptr;
 	struct __cgrps_kfunc_map_value *v;
@@ -217,11 +164,12 @@ int BPF_PROG(cgrp_kfunc_get_unreleased, struct cgroup *cgrp, const char *path)
 	if (!v)
 		return 0;
 
-	kptr = bpf_cgroup_kptr_get(&v->cgrp);
-	if (!kptr)
-		return 0;
-
-	/* Kptr acquired above is never released. */
+	bpf_rcu_read_lock();
+	kptr = v->cgrp;
+	if (kptr)
+		/* Can't release a cgroup kptr stored in a map. */
+		bpf_cgroup_release(kptr);
+	bpf_rcu_read_unlock();
 
 	return 0;
 }
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
index e9dbd1af05a7..5354455a01be 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
@@ -126,13 +126,11 @@ int BPF_PROG(test_cgrp_get_release, struct cgroup *cgrp, const char *path)
 		return 0;
 	}
 
-	kptr = bpf_cgroup_kptr_get(&v->cgrp);
-	if (!kptr) {
+	bpf_rcu_read_lock();
+	kptr = v->cgrp;
+	if (!kptr)
 		err = 3;
-		return 0;
-	}
-
-	bpf_cgroup_release(kptr);
+	bpf_rcu_read_unlock();
 
 	return 0;
 }