[Devel] [PATCH 2/2 v4] ve/cgroup: Added pointers to owning ve to root cgroups

[Valeriy Vdovin]

Follow-up patch to per-cgroup release_agent property. release_agent
notifications are spawned from a special kthread, running under ve0. But
newly spawned tasks should run under their own ve context. Easy way to
pass this information to a spawning thread is by adding 've_owner' field
to a root cgroup. At notification any cgroup can be walked upwards to
it's root and get ve_owner from there. ve_owner is initialized at container
start, that's when we know all cgroup ve roots for free. For ve0 roots
we don't need ve_owner field set, because we can always get pointer to ve0.
Only place where we can detch ve_owner knowledge from root ve cgroups is
at cgroup_exit for ve->init_task, because that's that's the last time, when
ve->init_task is related to it's ve root cgroups (see cgroup_exit comments).

https://jira.sw.ru/browse/PSBM-83887
Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
---
 include/linux/cgroup.h |  3 +++
 kernel/cgroup.c        | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5e289fc..34fc017 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -291,6 +291,9 @@ struct cgroup {
 	struct simple_xattrs xattrs;
 	u64 subgroups_limit;
 
+	/* ve_owner, responsible for running release agent. */
+	struct ve_struct *ve_owner;
+
 	/*
 	 * Per-cgroup path to release agent binary for release
 	 * notifications.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1d4605..31e7db6 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4352,6 +4352,7 @@ int cgroup_mark_ve_root(struct ve_struct *ve)
 	mutex_lock(&cgroup_mutex);
 	for_each_active_root(root) {
 		cgrp = task_cgroup_from_root(ve->init_task, root);
+		cgrp->ve_owner = ve;
 		set_bit(CGRP_VE_ROOT, &cgrp->flags);
 		err = cgroup_add_file_on_mark_ve(cgrp);
 		if (err)
@@ -4363,6 +4364,20 @@ int cgroup_mark_ve_root(struct ve_struct *ve)
 	return err;
 }
 
+static void cgroup_unbind_roots_from_ve(struct ve_struct *ve)
+{
+	struct cgroup *cgrp;
+	struct cgroupfs_root *root;
+
+	mutex_lock(&cgroup_mutex);
+	for_each_active_root(root) {
+		cgrp = task_cgroup_from_root(ve->init_task, root);
+		BUG_ON(!cgrp->ve_owner);
+		cgrp->ve_owner = NULL;
+	}
+	mutex_unlock(&cgroup_mutex);
+}
+
 struct cgroup *cgroup_get_ve_root(struct cgroup *cgrp)
 {
 	struct cgroup *ve_root = NULL;
@@ -5401,6 +5416,14 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 	int i;
 
 	/*
+	 * Detect that the task in question is ve->init_task
+	 * if so, unbind all cgroups that want to be released under
+	 * this ve.
+	 */
+	if (!ve_is_super(tsk->task_ve) && tsk == tsk->task_ve->init_task)
+		cgroup_unbind_roots_from_ve(tsk->task_ve);
+
+	/*
 	 * Unlink from the css_set task list if necessary.
 	 * Optimistically check cg_list before taking
 	 * css_set_lock
@@ -5493,6 +5516,7 @@ static void cgroup_release_agent(struct work_struct *work)
 	raw_spin_lock(&release_list_lock);
 	while (!list_empty(&release_list)) {
 		char *argv[3], *envp[3];
+		struct ve_struct *ve = NULL;
 		int i, err;
 		const char *release_agent;
 		char *pathbuf = NULL, *agentbuf = NULL;
@@ -5507,14 +5531,38 @@ static void cgroup_release_agent(struct work_struct *work)
 			goto continue_free;
 		if (__cgroup_path(cgrp, pathbuf, PAGE_SIZE, true) < 0)
 			goto continue_free;
+
+		/*
+		 * Deduce under which VE we are going to spawn nofitier
+		 * binary. Non-root VE has it's VE-local root cgroup,
+		 * marked with VE_ROOT flag. It has non-NULL ve_owner
+		 * set during cgroup_mark_ve_root.
+		 * VE0 root cgroup does not need ve_owner field, because
+		 * it's ve is ve0. Non-VE root cgroup does not have a parent.
+		 */
 		root_cgrp = cgroup_get_local_root(cgrp);
+		if (root_cgrp->parent == NULL)
+			ve = &ve0;
+		else
+			ve = root_cgrp->ve_owner;
+		if (!ve)
+			goto continue_free;
+
+		down_read(&ve->op_sem);
+		if (ve->is_running) {
+			up_read(&ve->op_sem);
+			goto continue_free;
+		}
+
 		rcu_read_lock();
+
 		release_agent = cgroup_release_agent_path(root_cgrp);
 		if (release_agent)
 			agentbuf = kstrdup(release_agent, GFP_KERNEL);
 		rcu_read_unlock();
 		if (!agentbuf)
 			goto continue_free;
+		get_ve(ve);
 
 		i = 0;
 		argv[i++] = agentbuf;
@@ -5530,12 +5578,20 @@ static void cgroup_release_agent(struct work_struct *work)
 		/* Drop the lock while we invoke the usermode helper,
 		 * since the exec could involve hitting disk and hence
 		 * be a slow process */
+
 		mutex_unlock(&cgroup_mutex);
+#ifdef CONFIG_VE
+		err = call_usermodehelper_fns_ve(ve, argv[0], argv,
+			envp, UMH_WAIT_EXEC, NULL, NULL, NULL);
+#else
 		err = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+#endif
 		if (err < 0)
 			pr_warn_ratelimited("cgroup release_agent "
 					    "%s %s failed: %d\n",
 					    agentbuf, pathbuf, err);
+		up_read(&ve->op_sem);
+		put_ve(ve);
 
 		mutex_lock(&cgroup_mutex);
  continue_free:
-- 
1.8.3.1