[Devel] [PATCH VZ8 v3 14/14] cgroup/ve: do not run release_agent on non-running ve

[Valeriy Vdovin]

cgroup1_release_agent is a function that runs within a private
ve workqueue. When exectured, it runs an executable in a userspace
by a call to call_usermodehelper_ve. There is conflict that when
ve is getting shutdown and some of last cgroups get's deleted at the
same time, the workqueue might still be running, but ve_stop_ns has
already been called. ve_stop_ns will stop usermode helper threads,
needed for call_usermodehelper_ve. Because of that a call to
call_usermodehelper_ve will never return, causing a hang.
To defeat that hang VZ7 code of call_usermodehelper_ve included the
check that ve is still running before running the userspace executable.
It also checked for ve->init_task->flags & PF_EXITING condition.
But in VZ8 the whole usermodehelper infrastructure is much more different.
Also VZ8 does not have ve->init_task in it's fields.
That's why it seems more relevant right now to do ve->is_running
check before the call to call_usermodehelper_ve.

Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
---
 kernel/cgroup/cgroup-v1.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 993ac38b895f..cd1a0df6c528 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -934,9 +934,12 @@ void cgroup1_release_agent(struct work_struct *work)
 		envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
 		envp[i] = NULL;
 
-
 		mutex_unlock(&cgroup_mutex);
 
+		down_write(&ve->op_sem);
+		if (!ve->is_running)
+			goto continue_with_mutex;
+
 		err = call_usermodehelper_ve(ve, argv[0], argv,
 			envp, UMH_WAIT_EXEC);
 
@@ -944,6 +947,7 @@ void cgroup1_release_agent(struct work_struct *work)
 			pr_warn_ratelimited("cgroup1_release_agent "
 					    "%s %s failed: %d\n",
 					    agentbuf, pathbuf, err);
+continue_with_mutex:
 		up_write(&ve->op_sem);
 		mutex_lock(&cgroup_mutex);
 continue_free:
-- 
2.27.0