[Devel] [PATCH RHEL8 COMMIT] ve: fix reading container state from cgroup

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.53
------>
commit 22b6ab88d5fcf9c0dd57e550fb1bf0c40544a085
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Fri Jul 9 19:39:48 2021 +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) add !ve->ve_ns check for showing STOPPED just to be more consistent
        with vz7 and don't show STOPPED if we still see non-null ve->ve_ns.
    
    So now we have:
    
    RUNNING                 | STOPPED
    is_running==true        | is_running==false
                            | ve_ns==NULL
                            | !cgroup_is_populated()
    
    Before these patch we were able to see STARTING instead of STOPPING and
    vice versa.
    
    https://jira.sw.ru/browse/PSBM-82766
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    rebase to vz8:
    Reworked:
     - bring back ve_ns check from vz7 for consistency
     - leave cgroup_is_populated as it looks like a valid replacement
       for nr_threads_ve
     - remove rcu_access_pointer as we are under ve->op_sem anyway
    
    https://jira.sw.ru/browse/PSBM-131412
    https://jira.sw.ru/browse/PSBM-127798
    
    (cherry-picked from vz7 commit 1c182ff3216c ("ve: fix reading container
    state from cgroup"))
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 kernel/ve/ve.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index 9667f9051c02..dc920cdf5921 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -1147,15 +1147,17 @@ static int ve_state_show(struct seq_file *sf, void *v)
 	struct cgroup_subsys_state *css = seq_css(sf);
 	struct ve_struct *ve = css_to_ve(css);
 
+	down_read(&ve->op_sem);
 	if (ve->is_running)
 		seq_puts(sf, "RUNNING");
-	else if (!cgroup_is_populated(css->cgroup))
+	else if (!cgroup_is_populated(css->cgroup) && !ve->ve_ns)
 		seq_puts(sf, "STOPPED");
-	else if (rcu_access_pointer(ve->ve_ns))
+	else if (ve->ve_ns)
 		seq_puts(sf, "STOPPING");
 	else
 		seq_puts(sf, "STARTING");
 	seq_putc(sf, '\n');
+	up_read(&ve->op_sem);
 
 	return 0;
 }