linux-kernel - [RFC PATCH bpf-next 6/9] cgroup: add v1 support to cgroup_get_from

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Message-Id: <20220510001807.4132027-7-yosryahmed@google.com>
Date:   Tue, 10 May 2022 00:18:04 +0000
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Stanislav Fomichev <sdf@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: [RFC PATCH bpf-next 6/9] cgroup: add v1 support to cgroup_get_from_id()

The current implementation of cgroup_get_from_id() only searches the
default hierarchy for the given id. Make it compatible with cgroup v1 by
looking through all the roots instead.

cgrp_dfl_root should be the first element in the list so there shouldn't
be a performance impact for cgroup v2 users (in the case of a valid id).

Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
---
 kernel/cgroup/cgroup.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index af703cfcb9d2..12700cd21973 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5970,10 +5970,16 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
  */
 struct cgroup *cgroup_get_from_id(u64 id)
 {
-	struct kernfs_node *kn;
+	struct kernfs_node *kn = NULL;
 	struct cgroup *cgrp = NULL;
+	struct cgroup_root *root;
+
+	for_each_root(root) {
+		kn = kernfs_find_and_get_node_by_id(root->kf_root, id);
+		if (kn)
+			break;
+	}
 
-	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
 	if (!kn)
 		goto out;
 
-- 
2.36.0.512.ge40c2bad7a-goog