[Devel] [PATCH RHEL7 COMMIT] ve: fix reading container state from cgroup

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.21.1.vz7.46.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.21.1.vz7.46.2
------>
commit 9e447b545df8bc5b4303dbed890309fd9ea4fbad
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Mon Apr 2 15:20:09 2018 +0300

    ve: fix reading container state from cgroup
    
    1) ve->op_sem is needed to remove race with ve_start_container when
    ve->is_running == 0 but ve->ve_ns != NULL already, and for a short
    moment we would print "STOPPING" if read state on container start
    
    2) replace !ve->init_task to !ve->ve_ns for simplicity they are changed
    synchronously under ve->op_sem anyway, so lets do all checks with ve_ns
    
    3) bring back !nr_threads_ve(ve) check as it is the only way we can
    discern "STOPPED" from "STARTING"
    
    So now we have:
    
    RUNNING                 | STOPPED
    is_running==true        | is_running==false
                            | ve_ns==NULL
                            | nr_threads_ve==0
    Before these patch we were able to see STARTING instead of STOPPING and
    vice versa.
    
    Note: bug started to reproduce after "ve: fix container stopped state
    check" part of commit 677f0715bb21 ("ve: initial patch").
    
    https://jira.sw.ru/browse/PSBM-82766
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 kernel/ve/ve.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index f562fb9e5cbf..88e1c4cc3700 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -858,15 +858,17 @@ static int ve_state_read(struct cgroup *cg, struct cftype *cft,
 {
 	struct ve_struct *ve = cgroup_ve(cg);
 
+	down_read(&ve->op_sem);
 	if (ve->is_running)
 		seq_puts(m, "RUNNING");
-	else if (!ve->init_task)
+	else if (!nr_threads_ve(ve) && !ve->ve_ns)
 		seq_puts(m, "STOPPED");
 	else if (ve->ve_ns)
 		seq_puts(m, "STOPPING");
 	else
 		seq_puts(m, "STARTING");
 	seq_putc(m, '\n');
+	up_read(&ve->op_sem);
 
 	return 0;
 }