2022-09-23 17:37:14

by Tejun Heo

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 <[email protected]>
Date: Fri, 23 Sep 2022 07:23:06 -1000
MIME-Version: 1.0
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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 <[email protected]>
Cc: Ming Lei <[email protected]>
Cc: Michal Koutn? <[email protected]>
---
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

2022-09-28 12:06:17

by Michal Koutný

Subject: Re: [PATCH cgroup/for-6.1] cgroup: Make cgroup_get_from_id() prettier

On Fri, Sep 23, 2022 at 07:31:58AM -1000, Tejun Heo <[email protected]> wrote:
> 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.

The cleanup looks good.

Just for the record, I understand the refernced fix is persisted as
> df02452f3df0 ("cgroup: cgroup_get_from_id() must check the looked-up kn is a directory")

Regards,
Michal