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@xxxxxxxxxxxxxx>
---
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
--
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