Merge branch 'for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - Waiman's cgroup2 cpuset support has been finally merged closing one
   of the last remaining feature gaps.

 - cgroup.procs could show non-leader threads when cgroup2 threaded mode
   was used in certain ways. I forgot to push the fix during the last
   cycle.

 - A patch to fix mount option parsing when all mount options have been
   consumed by someone else (LSM).

 - cgroup_no_v1 boot param can now block named cgroup1 hierarchies too.

* 'for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: Add named hierarchy disabling to cgroup_no_v1 boot param
  cgroup: fix parsing empty mount option string
  cpuset: Remove set but not used variable 'cs'
  cgroup: fix CSS_TASK_ITER_PROCS
  cgroup: Add .__DEBUG__. prefix to debug file names
  cpuset: Minor cgroup2 interface updates
  cpuset: Expose cpuset.cpus.subpartitions with cgroup_debug
  cpuset: Add documentation about the new "cpuset.sched.partition" flag
  cpuset: Use descriptive text when reading/writing cpuset.sched.partition
  cpuset: Expose cpus.effective and mems.effective on cgroup v2 root
  cpuset: Make generate_sched_domains() work with partition
  cpuset: Make CPU hotplug work with partition
  cpuset: Track cpusets that use parent's effective_cpus
  cpuset: Add an error state to cpuset.sched.partition
  cpuset: Add new v2 cpuset.sched.partition flag
  cpuset: Simply allocation and freeing of cpumasks
  cpuset: Define data structures to support scheduling partition
  cpuset: Enable cpuset controller in default hierarchy
  cgroup: remove unnecessary unlikely()

kernel/cgroup/cgroup.c

@@ -86,6 +86,7 @@ EXPORT_SYMBOL_GPL(css_set_lock);
 
 DEFINE_SPINLOCK(trace_cgroup_path_lock);
 char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
+bool cgroup_debug __read_mostly;
 
 /*
  * Protects cgroup_idr and css_idr so that IDs can be released without
@@ -1429,12 +1430,15 @@ static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
 	struct cgroup_subsys *ss = cft->ss;
 
 	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
-	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
-		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
-			 cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
+	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
+		const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";
+
+		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
+			 dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
 			 cft->name);
-	else
+	} else {
 		strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
+	}
 	return buf;
 }
 
@@ -1774,7 +1778,7 @@ static int parse_cgroup_root_flags(char *data, unsigned int *root_flags)
 
 	*root_flags = 0;
 
-	if (!data)
+	if (!data || *data == '\0')
 		return 0;
 
 	while ((token = strsep(&data, ",")) != NULL) {
@@ -3669,7 +3673,8 @@ restart:
 			continue;
 		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
 			continue;
-
+		if ((cft->flags & CFTYPE_DEBUG) && !cgroup_debug)
+			continue;
 		if (is_add) {
 			ret = cgroup_add_file(css, cgrp, cft);
 			if (ret) {
@@ -4232,20 +4237,25 @@ static void css_task_iter_advance(struct css_task_iter *it)
 
 	lockdep_assert_held(&css_set_lock);
 repeat:
-	/*
-	 * Advance iterator to find next entry.  cset->tasks is consumed
-	 * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
-	 * next cset.
-	 */
-	next = it->task_pos->next;
+	if (it->task_pos) {
+		/*
+		 * Advance iterator to find next entry.  cset->tasks is
+		 * consumed first and then ->mg_tasks.  After ->mg_tasks,
+		 * we move onto the next cset.
+		 */
+		next = it->task_pos->next;
 
-	if (next == it->tasks_head)
-		next = it->mg_tasks_head->next;
+		if (next == it->tasks_head)
+			next = it->mg_tasks_head->next;
 
-	if (next == it->mg_tasks_head)
+		if (next == it->mg_tasks_head)
+			css_task_iter_advance_css_set(it);
+		else
+			it->task_pos = next;
+	} else {
+		/* called from start, proceed to the first cset */
 		css_task_iter_advance_css_set(it);
-	else
-		it->task_pos = next;
+	}
 
 	/* if PROCS, skip over tasks which aren't group leaders */
 	if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
@@ -4285,7 +4295,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
 
 	it->cset_head = it->cset_pos;
 
-	css_task_iter_advance_css_set(it);
+	css_task_iter_advance(it);
 
 	spin_unlock_irq(&css_set_lock);
 }
@@ -5773,6 +5783,16 @@ static int __init cgroup_disable(char *str)
 }
 __setup("cgroup_disable=", cgroup_disable);
 
+void __init __weak enable_debug_cgroup(void) { }
+
+static int __init enable_cgroup_debug(char *str)
+{
+	cgroup_debug = true;
+	enable_debug_cgroup();
+	return 1;
+}
+__setup("cgroup_debug", enable_cgroup_debug);
+
 /**
  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
  * @dentry: directory dentry of interest
@@ -6008,10 +6028,8 @@ static ssize_t show_delegatable_files(struct cftype *files, char *buf,
 
 		ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
 
-		if (unlikely(ret >= size)) {
-			WARN_ON(1);
+		if (WARN_ON(ret >= size))
 			break;
-		}
 	}
 
 	return ret;