linux-kernel - [PATCH cgroup/for-6.1] cgroup: Make cgroup_get_from

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Message-ID: <Yy3tjvIGd2j4wnSw@slm.duckdns.org>
Date:   Fri, 23 Sep 2022 07:31:58 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Marco Patalano <mpatalan@...hat.com>,
        Muneendra <muneendra.kumar@...adcom.com>,
        Michal Koutný <mkoutny@...e.com>
Subject: [PATCH cgroup/for-6.1] cgroup: Make cgroup_get_from_id() prettier

>From 7e1eb5437d3c3fdb61d45378579aab383cafc694 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Fri, 23 Sep 2022 07:23:06 -1000
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

After merging 836ac87d ("cgroup: fix cgroup_get_from_id") into for-6.1, its
combination with two commits in for-6.1 - 4534dee9 ("cgroup: cgroup: Honor
caller's cgroup NS when resolving cgroup id") and fa7e439c ("cgroup:
Homogenize cgroup_get_from_id() return value") - makes the gotos in the
error handling path too ugly while not adding anything of value.

All that the gotos are saving is one extra kernfs_put() call. Let's remove
the gotos and perform error returns directly.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: Michal Koutný <mkoutny@...e.com>
---
Hello,

Ming, Michal, you guys' changes to cgroup_get_from_id() combine to make
cgroup_get_from_id() a bit too ugly, so I applied the following patch to
cgroup/for-6.1. Please take a look and lemme know if I broke anything.

Thanks.

 kernel/cgroup/cgroup.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 0d93cd17548c..c1f1ef6090da 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6066,14 +6066,16 @@ 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 cgroup *cgrp = NULL, *root_cgrp;
+	struct cgroup *cgrp, *root_cgrp;
 
 	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
 	if (!kn)
-		goto out;
+		return ERR_PTR(-ENOENT);
 
-	if (kernfs_type(kn) != KERNFS_DIR)
-		goto put;
+	if (kernfs_type(kn) != KERNFS_DIR) {
+		kernfs_put(kn);
+		return ERR_PTR(-ENOENT);
+	}
 
 	rcu_read_lock();
 
@@ -6082,21 +6084,20 @@ struct cgroup *cgroup_get_from_id(u64 id)
 		cgrp = NULL;
 
 	rcu_read_unlock();
-put:
 	kernfs_put(kn);
 
 	if (!cgrp)
-		goto out;
+		return ERR_PTR(-ENOENT);
 
 	spin_lock_irq(&css_set_lock);
 	root_cgrp = current_cgns_cgroup_from_root(&cgrp_dfl_root);
 	spin_unlock_irq(&css_set_lock);
 	if (!cgroup_is_descendant(cgrp, root_cgrp)) {
 		cgroup_put(cgrp);
-		cgrp = NULL;
+		return ERR_PTR(-ENOENT);
 	}
-out:
-	return cgrp ?: ERR_PTR(-ENOENT);
+
+	return cgrp;
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_id);
 
-- 
2.37.3