From c7d97dde89ddb2fc40f077705052762d91c35040 Mon Sep 17 00:00:00 2001
From: "Costa Tsaousis (ktsaou)" <costa@tsaousis.gr>
Date: Sat, 3 Sep 2016 00:40:14 +0300
Subject: [PATCH] keep track of duplicate cgroups (cgroups with same name) and
 enable the first available when any cgroup is removed; fixes #874

---
 src/sys_fs_cgroup.c | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/src/sys_fs_cgroup.c b/src/sys_fs_cgroup.c
index b972ed12..fe9bbc47 100644
--- a/src/sys_fs_cgroup.c
+++ b/src/sys_fs_cgroup.c
@@ -160,9 +160,12 @@ struct cpuacct_usage {
     unsigned long long *cpu_percpu;
 };
 
+#define CGROUP_OPTIONS_DISABLED_DUPLICATE 0x00000001
+
 struct cgroup {
+    uint32_t options;
+
     char available;      // found in the filesystem
-    char last_available; // found in the filesystem the last time
     char enabled;        // enabled in the config
 
     char *id;
@@ -715,18 +718,18 @@ struct cgroup *cgroup_add(const char *id) {
                 if (!strncmp(t->chart_id, "/system.slice/", 14) && !strncmp(cg->chart_id, "/init.scope/system.slice/", 25)) {
                     error("Control group with chart id '%s' already exists with id '%s' and is enabled. Swapping them by enabling cgroup with id '%s' and disabling cgroup with id '%s'.",
                           cg->chart_id, t->id, cg->id, t->id);
+                    debug(D_CGROUP, "Control group with chart id '%s' already exists with id '%s' and is enabled. Swapping them by enabling cgroup with id '%s' and disabling cgroup with id '%s'.",
+                          cg->chart_id, t->id, cg->id, t->id);
                     t->enabled = 0;
-                } else {
-                    if(t->last_available) {
-                        error("Control group with chart id '%s' already exists with id '%s' and is enabled and available. Disabling cgroup with id '%s'.",
-                              cg->chart_id, t->id, cg->id);
-                        cg->enabled = 0;
-                    }
-                    else {
-                        error("Control group with chart id '%s' already exists with id '%s' but is not available. Enabling cgroup with id '%s'.",
-                              cg->chart_id, t->id, cg->id);
-                        t->enabled = 0;
-                    }
+                    t->options |= CGROUP_OPTIONS_DISABLED_DUPLICATE;
+                }
+                else {
+                    error("Control group with chart id '%s' already exists with id '%s' and is enabled and available. Disabling cgroup with id '%s'.",
+                          cg->chart_id, t->id, cg->id);
+                    debug(D_CGROUP, "Control group with chart id '%s' already exists with id '%s' and is enabled and available. Disabling cgroup with id '%s'.",
+                          cg->chart_id, t->id, cg->id);
+                    cg->enabled = 0;
+                    cg->options |= CGROUP_OPTIONS_DISABLED_DUPLICATE;
                 }
 
                 break;
@@ -874,7 +877,6 @@ void mark_all_cgroups_as_not_available() {
 
     // mark all as not available
     for(cg = cgroup_root; cg ; cg = cg->next) {
-        cg->last_available = cg->available;
         cg->available = 0;
     }
 }
@@ -884,6 +886,18 @@ void cleanup_all_cgroups() {
 
     for(; cg ;) {
         if(!cg->available) {
+            // enable the first duplicate cgroup
+            {
+                struct cgroup *t;
+                for(t = cgroup_root; t ; t = t->next) {
+                    if(t != cg && t->available && !t->enabled && t->options & CGROUP_OPTIONS_DISABLED_DUPLICATE && t->hash_chart == cg->hash_chart && !strcmp(t->chart_id, cg->chart_id)) {
+                        debug(D_CGROUP, "Enabling duplicate of cgroup '%s' with id '%s', because the original with id '%s' stopped.", t->chart_id, t->id, cg->id);
+                        t->enabled = 1;
+                        t->options &= ~CGROUP_OPTIONS_DISABLED_DUPLICATE;
+                        break;
+                    }
+                }
+            }
 
             if(!last)
                 cgroup_root = cg->next;
-- 
2.39.2