[RFC PATCH-cgroup 5/6] cgroup: Skip dying css in cgroup_apply_control_{enable,disable}

Waiman Long
2017-06-14T15:05:36Z

While constantly turning on and off controllers, it is possible to
trigger the dying CSS warnings in cgroup_apply_control_enable() and
cgroup_apply_control_disable(). The current code, however, proceeds
after the warning leading to other secondary warnings and maybe even
data corruption, like

cgroup: cgroup_addrm_files: failed to add current, err=-17

To avoid the secondary errors, the dying CSS is now ignored or skipped
so as not to cause other problem.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cgroup.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index f0bea32..2a5bd49 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2846,12 +2846,24 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp)
for_each_subsys(ss, ssid) {
struct cgroup_subsys_state *css = cgroup_css(dsct, ss);

- WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
-
if (!(cgroup_ss_mask(dsct, false) & (1 << ss->id)) ||
(dsct->bypass_ss_mask & (1 << ss->id)))
continue;

+ /*
+ * If the css is dying, we will just skip it after
+ * warning.
+ */
+ if (css && (css->flags & CSS_DYING)) {
+ char name[NAME_MAX+1];
+
+ cgroup_name(cgrp, name, NAME_MAX);
+ pr_warn("%s: %s css of cgroup %s is dying!\n",
+ __func__, ss->name, name);
+ WARN_ON_ONCE(1);
+ continue;
+ }
+
if (!css) {
css = css_create(dsct, ss);
if (IS_ERR(css))
@@ -2893,9 +2905,7 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp)
for_each_subsys(ss, ssid) {
struct cgroup_subsys_state *css = cgroup_css(dsct, ss);

- WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
-
- if (!css)
+ if (!css || (css->flags & CSS_DYING))
continue;

if (css->parent &&
--
1.8.3.1