[PATCH] cgroup: Introduce cgroup_detach_task().

[PATCH] cgroup: Introduce cgroup_detach_task().

[Dongsheng Yang]

Currently, the only method to detach a task from a cgroup is moving
it to others. It looks not natrual to me.

Inspired by cgroup_subtree_control_write(), this patch introduce allow
user to at-detach a process to/from a cgroup by echo "+/-pid" to
cgroup.procs. In addition, we keep the old method to allow user
echo "pid" without "+/-" to cgroup.procs as a attaching behavior.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 kernel/cgroup.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 60 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7dc8788..11ef4ac 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2348,6 +2348,43 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
 	return ret;
 }
 
+/**
+ * cgroup_detach_task - detach a task or a whole threadgroup to a cgroup
+ * @src_cgrp: the cgroup to detach from
+ * @leader: the task or the leader of the threadgroup to be attached
+ * @threadgroup: attach the whole threadgroup?
+ *
+ * Call holding cgroup_mutex and threadgroup_lock of @leader.
+ */
+static int cgroup_detach_task(struct cgroup *src_cgrp __maybe_unused,
+			      struct task_struct *leader, bool threadgroup)
+{
+	LIST_HEAD(preloaded_csets);
+	struct task_struct *task;
+	int ret;
+
+	/* look up all src csets */
+	down_read(&css_set_rwsem);
+	rcu_read_lock();
+	task = leader;
+	do {
+		cgroup_migrate_add_src(task_css_set(task), &cgrp_dfl_root.cgrp,
+				       &preloaded_csets);
+		if (!threadgroup)
+			break;
+	} while_each_thread(leader, task);
+	rcu_read_unlock();
+	up_read(&css_set_rwsem);
+
+	/* prepare dst csets and commit */
+	ret = cgroup_migrate_prepare_dst(&cgrp_dfl_root.cgrp, &preloaded_csets);
+	if (!ret)
+		ret = cgroup_migrate(&cgrp_dfl_root.cgrp, leader, threadgroup);
+
+	cgroup_migrate_finish(&preloaded_csets);
+	return ret;
+}
+
 /*
  * Find the task_struct of the task to attach by vpid and pass it along to the
  * function to attach either it or all tasks in its threadgroup. Will lock
@@ -2361,8 +2398,26 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
 	struct cgroup *cgrp;
 	pid_t pid;
 	int ret;
+	bool attach;
 
-	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+	/*
+	 * Parse input - space separated list of subsystem names prefixed
+	 * with either + or -.
+	 */
+	buf = strstrip(buf);
+	if (*buf == '+') {
+		attach = true;
+		buf++;
+	} else if (*buf == '-') {
+		attach = false;
+		buf++;
+	} else {
+		if (!isdigit(*buf))
+			return -EINVAL;
+		attach = true;
+	}
+
+	if (kstrtoint(buf, 0, &pid) || pid < 0)
 		return -EINVAL;
 
 	cgrp = cgroup_kn_lock_live(of->kn);
@@ -2426,7 +2481,10 @@ retry_find_task:
 		}
 	}
 
-	ret = cgroup_attach_task(cgrp, tsk, threadgroup);
+	if (attach)
+		ret = cgroup_attach_task(cgrp, tsk, threadgroup);
+	else
+		ret = cgroup_detach_task(cgrp, tsk, threadgroup);
 
 	threadgroup_unlock(tsk);
 
-- 
1.8.4.2

Re: [PATCH] cgroup: Introduce cgroup_detach_task().

[Dongsheng Yang]

Sorry for the noise, :(.

This patch is not a correct version. Please ignore it and I have sent a 
v2 for it.

Thanx

On 08/25/2014 07:28 PM, Dongsheng Yang wrote:
> Currently, the only method to detach a task from a cgroup is moving
> it to others. It looks not natrual to me.
>
> Inspired by cgroup_subtree_control_write(), this patch introduce allow
> user to at-detach a process to/from a cgroup by echo "+/-pid" to
> cgroup.procs. In addition, we keep the old method to allow user
> echo "pid" without "+/-" to cgroup.procs as a attaching behavior.
>
> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
> ---
>   kernel/cgroup.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 60 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 7dc8788..11ef4ac 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2348,6 +2348,43 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
>   	return ret;
>   }
>   
> +/**
> + * cgroup_detach_task - detach a task or a whole threadgroup to a cgroup
> + * @src_cgrp: the cgroup to detach from
> + * @leader: the task or the leader of the threadgroup to be attached
> + * @threadgroup: attach the whole threadgroup?
> + *
> + * Call holding cgroup_mutex and threadgroup_lock of @leader.
> + */
> +static int cgroup_detach_task(struct cgroup *src_cgrp __maybe_unused,
> +			      struct task_struct *leader, bool threadgroup)
> +{
> +	LIST_HEAD(preloaded_csets);
> +	struct task_struct *task;
> +	int ret;
> +
> +	/* look up all src csets */
> +	down_read(&css_set_rwsem);
> +	rcu_read_lock();
> +	task = leader;
> +	do {
> +		cgroup_migrate_add_src(task_css_set(task), &cgrp_dfl_root.cgrp,
> +				       &preloaded_csets);
> +		if (!threadgroup)
> +			break;
> +	} while_each_thread(leader, task);
> +	rcu_read_unlock();
> +	up_read(&css_set_rwsem);
> +
> +	/* prepare dst csets and commit */
> +	ret = cgroup_migrate_prepare_dst(&cgrp_dfl_root.cgrp, &preloaded_csets);
> +	if (!ret)
> +		ret = cgroup_migrate(&cgrp_dfl_root.cgrp, leader, threadgroup);
> +
> +	cgroup_migrate_finish(&preloaded_csets);
> +	return ret;
> +}
> +
>   /*
>    * Find the task_struct of the task to attach by vpid and pass it along to the
>    * function to attach either it or all tasks in its threadgroup. Will lock
> @@ -2361,8 +2398,26 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
>   	struct cgroup *cgrp;
>   	pid_t pid;
>   	int ret;
> +	bool attach;
>   
> -	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
> +	/*
> +	 * Parse input - space separated list of subsystem names prefixed
> +	 * with either + or -.
> +	 */
> +	buf = strstrip(buf);
> +	if (*buf == '+') {
> +		attach = true;
> +		buf++;
> +	} else if (*buf == '-') {
> +		attach = false;
> +		buf++;
> +	} else {
> +		if (!isdigit(*buf))
> +			return -EINVAL;
> +		attach = true;
> +	}
> +
> +	if (kstrtoint(buf, 0, &pid) || pid < 0)
>   		return -EINVAL;
>   
>   	cgrp = cgroup_kn_lock_live(of->kn);
> @@ -2426,7 +2481,10 @@ retry_find_task:
>   		}
>   	}
>   
> -	ret = cgroup_attach_task(cgrp, tsk, threadgroup);
> +	if (attach)
> +		ret = cgroup_attach_task(cgrp, tsk, threadgroup);
> +	else
> +		ret = cgroup_detach_task(cgrp, tsk, threadgroup);
>   
>   	threadgroup_unlock(tsk);
>