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

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Hi,

On 10/29/2023 2:14 PM, Yafang Shao wrote:
> 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.
>
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
>  include/linux/cgroup.h          |  4 +++-
>  kernel/cgroup/cgroup-internal.h |  1 -
>  kernel/cgroup/cgroup-v1.c       | 33 +++++++++++++++++++++++++++++++++
>  3 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index b307013..e063e4c 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -71,6 +71,7 @@ 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>
> @@ -388,7 +389,6 @@ 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() ||				\
> @@ -855,4 +855,6 @@ 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 5e17f01..520b90d 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 c487ffe..f41767f 100644
> --- a/kernel/cgroup/cgroup-v1.c
> +++ b/kernel/cgroup/cgroup-v1.c
> @@ -1263,6 +1263,39 @@ 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;
> +
> +	rcu_read_lock();
> +	for_each_root(root) {
> +		/* cgroup1 only*/
> +		if (root == &cgrp_dfl_root)
> +			continue;
> +		if (root->hierarchy_id != hierarchy_id)
> +			continue;
> +		spin_lock_irq(&css_set_lock);

Considering that the kfunc may be called under IRQ context, should we
use spin_lock_irqsave instead ?
> +		cgrp = task_cgroup_from_root(tsk, root);
> +		if (!cgrp || !cgroup_tryget(cgrp))
> +			cgrp = ERR_PTR(-ENOENT);
> +		spin_unlock_irq(&css_set_lock);
> +		break;
> +	}
> +	rcu_read_unlock();
> +	return cgrp;
> +}
> +
>  static int __init cgroup1_wq_init(void)
>  {
>  	/*





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