2 files changed, 37 insertions, 10 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75c0ff00aca6..33a2f63d4a10 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -61,7 +61,6 @@
 #include <linux/cpuset.h>
 #include <linux/proc_ns.h>
 #include <linux/nsproxy.h>
-#include <linux/proc_ns.h>
 #include <net/sock.h>
 
 /*
@@ -1160,18 +1159,12 @@ static void cgroup_exit_root_id(struct cgroup_root *root)
 {
         lockdep_assert_held(&cgroup_mutex);
 
-        if (root->hierarchy_id) {
-                idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
-                root->hierarchy_id = 0;
-        }
+        idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
 }
 
 static void cgroup_free_root(struct cgroup_root *root)
 {
         if (root) {
-                /* hierarchy ID should already have been released */
-                WARN_ON_ONCE(root->hierarchy_id);
-
                 idr_destroy(&root->cgroup_idr);
                 kfree(root);
         }
@@ -5146,6 +5139,8 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
         lockdep_assert_held(&cgroup_mutex);
 
         css = ss->css_alloc(parent_css);
+        if (!css)
+                css = ERR_PTR(-ENOMEM);
         if (IS_ERR(css))
                 return css;
 
@@ -6172,7 +6167,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
 {
         WARN_ON_ONCE(!rcu_read_lock_held());
-        return id > 0 ? idr_find(&ss->css_idr, id) : NULL;
+        return idr_find(&ss->css_idr, id);
 }
 
 /**
diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
index 303097b37429..2bd673783f1a 100644
--- a/kernel/cgroup_pids.c
+++ b/kernel/cgroup_pids.c
@@ -49,6 +49,12 @@ struct pids_cgroup {
          */
         atomic64_t                      counter;
         int64_t                         limit;
+
+        /* Handle for "pids.events" */
+        struct cgroup_file              events_file;
+
+        /* Number of times fork failed because limit was hit. */
+        atomic64_t                      events_limit;
 };
 
 static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
@@ -72,6 +78,7 @@ pids_css_alloc(struct cgroup_subsys_state *parent)
 
         pids->limit = PIDS_MAX;
         atomic64_set(&pids->counter, 0);
+        atomic64_set(&pids->events_limit, 0);
         return &pids->css;
 }
 
@@ -213,10 +220,21 @@ static int pids_can_fork(struct task_struct *task)
 {
         struct cgroup_subsys_state *css;
         struct pids_cgroup *pids;
+        int err;
 
         css = task_css_check(current, pids_cgrp_id, true);
         pids = css_pids(css);
-        return pids_try_charge(pids, 1);
+        err = pids_try_charge(pids, 1);
+        if (err) {
+                /* Only log the first time events_limit is incremented. */
+                if (atomic64_inc_return(&pids->events_limit) == 1) {
+                        pr_info("cgroup: fork rejected by pids controller in ");
+                        pr_cont_cgroup_path(task_cgroup(current, pids_cgrp_id));
+                        pr_cont("\n");
+                }
+                cgroup_file_notify(&pids->events_file);
+        }
+        return err;
 }
 
 static void pids_cancel_fork(struct task_struct *task)
@@ -288,6 +306,14 @@ static s64 pids_current_read(struct cgroup_subsys_state *css,
         return atomic64_read(&pids->counter);
 }
 
+static int pids_events_show(struct seq_file *sf, void *v)
+{
+        struct pids_cgroup *pids = css_pids(seq_css(sf));
+
+        seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events_limit));
+        return 0;
+}
+
 static struct cftype pids_files[] = {
         {
                 .name = "max",
@@ -300,6 +326,12 @@ static struct cftype pids_files[] = {
                 .read_s64 = pids_current_read,
                 .flags = CFTYPE_NOT_ON_ROOT,
         },
+        {
+                .name = "events",
+                .seq_show = pids_events_show,
+                .file_offset = offsetof(struct pids_cgroup, events_file),
+                .flags = CFTYPE_NOT_ON_ROOT,
+        },
         { }     /* terminate */
 };