[PATCH 1/4 v3] cgroup: use separate rstat api for bpf programs

[JP Kobryn <inwardvessel@gmail.com>]

The rstat updated/flush API functions are exported as kfuncs so bpf
programs can make the same calls that in-kernel code can. Split these API
functions into separate in-kernel and bpf versions. Function signatures
remain unchanged. The kfuncs are named with the prefix "bpf_". This
non-functional change allows for future commits which will modify the
signature of the in-kernel API without impacting bpf call sites. The
implementations of the kfuncs serve as adapters to the in-kernel API.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
---
 include/linux/cgroup.h                        |  3 +++
 kernel/cgroup/rstat.c                         | 19 ++++++++++++++-----
 .../bpf/progs/cgroup_hierarchical_stats.c     |  8 ++++----
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f8ef47f8a634..13fd82a4336d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -692,6 +692,9 @@ void cgroup_rstat_flush(struct cgroup *cgrp);
 void cgroup_rstat_flush_hold(struct cgroup *cgrp);
 void cgroup_rstat_flush_release(struct cgroup *cgrp);
 
+void bpf_cgroup_rstat_updated(struct cgroup *cgrp, int cpu);
+void bpf_cgroup_rstat_flush(struct cgroup *cgrp);
+
 /*
  * Basic resource stats.
  */
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index aac91466279f..0d66cfc53061 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -82,7 +82,7 @@ void _cgroup_rstat_cpu_unlock(raw_spinlock_t *cpu_lock, int cpu,
  * rstat_cpu->updated_children list.  See the comment on top of
  * cgroup_rstat_cpu definition for details.
  */
-__bpf_kfunc void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
+void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
 {
 	raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
 	unsigned long flags;
@@ -129,6 +129,11 @@ __bpf_kfunc void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
 	_cgroup_rstat_cpu_unlock(cpu_lock, cpu, cgrp, flags, true);
 }
 
+__bpf_kfunc void bpf_cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
+{
+	cgroup_rstat_updated(cgrp, cpu);
+}
+
 /**
  * cgroup_rstat_push_children - push children cgroups into the given list
  * @head: current head of the list (= subtree root)
@@ -346,7 +351,7 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp)
  *
  * This function may block.
  */
-__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)
+void cgroup_rstat_flush(struct cgroup *cgrp)
 {
 	might_sleep();
 
@@ -355,6 +360,11 @@ __bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)
 	__cgroup_rstat_unlock(cgrp, -1);
 }
 
+__bpf_kfunc void bpf_cgroup_rstat_flush(struct cgroup *cgrp)
+{
+	cgroup_rstat_flush(cgrp);
+}
+
 /**
  * cgroup_rstat_flush_hold - flush stats in @cgrp's subtree and hold
  * @cgrp: target cgroup
@@ -644,10 +654,9 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq)
 	cgroup_force_idle_show(seq, &cgrp->bstat);
 }
 
-/* Add bpf kfuncs for cgroup_rstat_updated() and cgroup_rstat_flush() */
 BTF_KFUNCS_START(bpf_rstat_kfunc_ids)
-BTF_ID_FLAGS(func, cgroup_rstat_updated)
-BTF_ID_FLAGS(func, cgroup_rstat_flush, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_cgroup_rstat_updated)
+BTF_ID_FLAGS(func, bpf_cgroup_rstat_flush, KF_SLEEPABLE)
 BTF_KFUNCS_END(bpf_rstat_kfunc_ids)
 
 static const struct btf_kfunc_id_set bpf_rstat_kfunc_set = {
diff --git a/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
index c74362854948..24450dd4d3f3 100644
--- a/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
+++ b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
@@ -37,8 +37,8 @@ struct {
 	__type(value, struct attach_counter);
 } attach_counters SEC(".maps");
 
-extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __ksym;
-extern void cgroup_rstat_flush(struct cgroup *cgrp) __ksym;
+extern void bpf_cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __ksym;
+extern void bpf_cgroup_rstat_flush(struct cgroup *cgrp) __ksym;
 
 static uint64_t cgroup_id(struct cgroup *cgrp)
 {
@@ -75,7 +75,7 @@ int BPF_PROG(counter, struct cgroup *dst_cgrp, struct task_struct *leader,
 	else if (create_percpu_attach_counter(cg_id, 1))
 		return 0;
 
-	cgroup_rstat_updated(dst_cgrp, bpf_get_smp_processor_id());
+	bpf_cgroup_rstat_updated(dst_cgrp, bpf_get_smp_processor_id());
 	return 0;
 }
 
@@ -141,7 +141,7 @@ int BPF_PROG(dumper, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 		return 1;
 
 	/* Flush the stats to make sure we get the most updated numbers */
-	cgroup_rstat_flush(cgrp);
+	bpf_cgroup_rstat_flush(cgrp);
 
 	total_counter = bpf_map_lookup_elem(&attach_counters, &cg_id);
 	if (!total_counter) {
-- 
2.47.1