linux-kernel - [PATCH 5/5 cgroup/for-6.16-fixes] cgroup: break up the internal rstat init/exit logic by subsys and base

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Message-ID: <20250722014030.297537-6-inwardvessel@gmail.com>
Date: Mon, 21 Jul 2025 18:40:30 -0700
From: JP Kobryn <inwardvessel@...il.com>
To: tj@...nel.org,
	shakeel.butt@...ux.dev,
	mkoutny@...e.com,
	yosryahmed@...gle.com,
	hannes@...xchg.org,
	akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	kernel-team@...a.com
Subject: [PATCH 5/5 cgroup/for-6.16-fixes] cgroup: break up the internal rstat init/exit logic by subsys and base

The __css_rstat_{base_,}init/exit() functions have complexity in how they
distinguish between base stats and formal subsystem stats. Eliminate this
complexity by breaking up these functions and moving the logic for base and
subsystem directly into their respective public API functions.

Signed-off-by: JP Kobryn <inwardvessel@...il.com>
---
 kernel/cgroup/rstat.c | 72 ++++++++++++++++++-------------------------
 1 file changed, 30 insertions(+), 42 deletions(-)

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index ba656a53136a..30fdf92a21a4 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -437,29 +437,15 @@ __bpf_kfunc void css_rstat_flush(struct cgroup_subsys_state *css)
 	}
 }
 
-static int __css_rstat_init(struct cgroup_subsys_state *css, bool is_self)
+int css_rstat_init(struct cgroup_subsys_state *css)
 {
-	struct cgroup *cgrp = css->cgroup;
 	int cpu;
 
-	if (is_self) {
-		/* the root cgrp has rstat_base_cpu preallocated */
-		if (!cgrp->rstat_base_cpu) {
-			cgrp->rstat_base_cpu = alloc_percpu(struct cgroup_rstat_base_cpu);
-			if (!cgrp->rstat_base_cpu)
-				return -ENOMEM;
-		}
-	}
-
 	/* the root cgrp's self css has rstat_cpu preallocated */
 	if (!css->rstat_cpu) {
 		css->rstat_cpu = alloc_percpu(struct css_rstat_cpu);
-		if (!css->rstat_cpu) {
-			if (is_self)
-				free_percpu(cgrp->rstat_base_cpu);
-
+		if (!css->rstat_cpu)
 			return -ENOMEM;
-		}
 	}
 
 	/* ->updated_children list is self terminated */
@@ -467,19 +453,12 @@ static int __css_rstat_init(struct cgroup_subsys_state *css, bool is_self)
 		struct css_rstat_cpu *rstatc = css_rstat_cpu(css, cpu);
 
 		rstatc->updated_children = css;
-
-		if (is_self) {
-			struct cgroup_rstat_base_cpu *rstatbc;
-
-			rstatbc = cgroup_rstat_base_cpu(cgrp, cpu);
-			u64_stats_init(&rstatbc->bsync);
-		}
 	}
 
 	return 0;
 }
 
-static void __css_rstat_exit(struct cgroup_subsys_state *css, bool is_self)
+void css_rstat_exit(struct cgroup_subsys_state *css)
 {
 	int cpu;
 
@@ -494,35 +473,44 @@ static void __css_rstat_exit(struct cgroup_subsys_state *css, bool is_self)
 			return;
 	}
 
-	if (is_self) {
-		struct cgroup *cgrp = css->cgroup;
-
-		free_percpu(cgrp->rstat_base_cpu);
-		cgrp->rstat_base_cpu = NULL;
-	}
-
 	free_percpu(css->rstat_cpu);
 	css->rstat_cpu = NULL;
 }
 
-int css_rstat_init(struct cgroup_subsys_state *css)
+int cgroup_rstat_base_init(struct cgroup *cgrp)
 {
-	return __css_rstat_init(css, false);
-}
+	int ret, cpu;
 
-void css_rstat_exit(struct cgroup_subsys_state *css)
-{
-	return __css_rstat_exit(css, false);
-}
+	/* the root cgrp has rstat_base_cpu preallocated */
+	if (!cgrp->rstat_base_cpu) {
+		cgrp->rstat_base_cpu = alloc_percpu(struct cgroup_rstat_base_cpu);
+		if (!cgrp->rstat_base_cpu)
+			return -ENOMEM;
+	}
 
-int cgroup_rstat_base_init(struct cgroup *cgrp)
-{
-	return __css_rstat_init(&cgrp->self, true);
+	ret = css_rstat_init(&cgrp->self);
+	if (ret) {
+		free_percpu(cgrp->rstat_base_cpu);
+		return ret;
+	}
+
+	/* ->updated_children list is self terminated */
+	for_each_possible_cpu(cpu) {
+		struct cgroup_rstat_base_cpu *rstatbc;
+
+		rstatbc = cgroup_rstat_base_cpu(cgrp, cpu);
+		u64_stats_init(&rstatbc->bsync);
+	}
+
+	return ret;
 }
 
 void cgroup_rstat_base_exit(struct cgroup *cgrp)
 {
-	__css_rstat_exit(&cgrp->self, true);
+	css_rstat_exit(&cgrp->self);
+
+	free_percpu(cgrp->rstat_base_cpu);
+	cgrp->rstat_base_cpu = NULL;
 }
 
 /**
-- 
2.47.1