Re: [PATCH v3 bpf-next 05/11] cgroup: Add a new helper for cgroup1 hierarchy

Tejun Heo
2023-11-09T23:30:20Z

Hello,

The following is the version updated to use irqsave/restore applied to
cgroup/for-6.8-bpf.

Thanks.
--- 8< ---
From aecd408b7e50742868b3305c24325a89024e2a30 Mon Sep 17 00:00:00 2001
From: Yafang Shao <laoar.shao@gmail.com>
Date: Sun, 29 Oct 2023 06:14:32 +0000
Subject: [PATCH] cgroup: Add a new helper for cgroup1 hierarchy

A new helper is added for cgroup1 hierarchy:

- task_get_cgroup1
Acquires the associated cgroup of a task within a specific cgroup1
hierarchy. The cgroup1 hierarchy is identified by its hierarchy ID.

This helper function is added to facilitate the tracing of tasks within
a particular container or cgroup dir in BPF programs. It's important to
note that this helper is designed specifically for cgroup1 only.

tj: Use irsqsave/restore as suggested by Hou Tao <houtao@huaweicloud.com>.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Hou Tao <houtao@huaweicloud.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/cgroup.h | 4 +++-
kernel/cgroup/cgroup-internal.h | 1 -
kernel/cgroup/cgroup-v1.c | 34 +++++++++++++++++++++++++++++++++
3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0ef0af66080e..34aaf0e87def 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -69,6 +69,7 @@ struct css_task_iter {
extern struct file_system_type cgroup_fs_type;
extern struct cgroup_root cgrp_dfl_root;
extern struct css_set init_css_set;
+extern spinlock_t css_set_lock;

#define SUBSYS(_x) extern struct cgroup_subsys _x ## _cgrp_subsys;
#include <linux/cgroup_subsys.h>
@@ -386,7 +387,6 @@ static inline void cgroup_unlock(void)
* as locks used during the cgroup_subsys::attach() methods.
*/
#ifdef CONFIG_PROVE_RCU
-extern spinlock_t css_set_lock;
#define task_css_set_check(task, __c) \
rcu_dereference_check((task)->cgroups, \
rcu_read_lock_sched_held() || \
@@ -853,4 +853,6 @@ static inline void cgroup_bpf_put(struct cgroup *cgrp) {}

#endif /* CONFIG_CGROUP_BPF */

+struct cgroup *task_get_cgroup1(struct task_struct *tsk, int hierarchy_id);
+
#endif /* _LINUX_CGROUP_H */
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 5e17f01ced9f..520b90dd97ec 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -164,7 +164,6 @@ struct cgroup_mgctx {
#define DEFINE_CGROUP_MGCTX(name) \
struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name)

-extern spinlock_t css_set_lock;
extern struct cgroup_subsys *cgroup_subsys[];
extern struct list_head cgroup_roots;

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 76db6c67e39a..04d11a7dd95f 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -1262,6 +1262,40 @@ int cgroup1_get_tree(struct fs_context *fc)
return ret;
}

+/**
+ * task_get_cgroup1 - Acquires the associated cgroup of a task within a
+ * specific cgroup1 hierarchy. The cgroup1 hierarchy is identified by its
+ * hierarchy ID.
+ * @tsk: The target task
+ * @hierarchy_id: The ID of a cgroup1 hierarchy
+ *
+ * On success, the cgroup is returned. On failure, ERR_PTR is returned.
+ * We limit it to cgroup1 only.
+ */
+struct cgroup *task_get_cgroup1(struct task_struct *tsk, int hierarchy_id)
+{
+ struct cgroup *cgrp = ERR_PTR(-ENOENT);
+ struct cgroup_root *root;
+ unsigned long flags;
+
+ rcu_read_lock();
+ for_each_root(root) {
+ /* cgroup1 only*/
+ if (root == &cgrp_dfl_root)
+ continue;
+ if (root->hierarchy_id != hierarchy_id)
+ continue;
+ spin_lock_irqsave(&css_set_lock, flags);
+ cgrp = task_cgroup_from_root(tsk, root);
+ if (!cgrp || !cgroup_tryget(cgrp))
+ cgrp = ERR_PTR(-ENOENT);
+ spin_unlock_irqrestore(&css_set_lock, flags);
+ break;
+ }
+ rcu_read_unlock();
+ return cgrp;
+}
+
static int __init cgroup1_wq_init(void)
{
/*
--
2.42.0