[PATCHSET] cgroup: Make debug controller useful for debugging

[PATCHSET] cgroup: Make debug controller useful for debugging

[Tejun Heo]

Hello, Waiman.

I dropped the thread mode part of the patches so that these aren't
blocked on thread mode, made the debug controller an implicit one on
cgroup2 which is enabled by "cgroup_debug" boot param (we can't mask
it on cgroup1 with the boot param at this point), and fixed the
lockdep warnings.

I applied the updated patches + follow up changes to cgroup/for-4.13.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-4.13

I'd really appreciate if you can go over the patches and check that I
didn't do anything stupid.

Thanks.

--
tejun

[PATCH 1/7] cgroup: Keep accurate count of tasks in each css_set

[Tejun Heo]

From: Waiman Long <longman@redhat.com>

The reference count in the css_set data structure was used as a
proxy of the number of tasks attached to that css_set. However, that
count is actually not an accurate measure especially with thread mode
support. So a new variable nr_tasks is added to the css_set to keep
track of the actual task count. This new variable is protected by
the css_set_lock. Functions that require the actual task count are
updated to use the new variable.

tj: s/task_count/nr_tasks/ for consistency with cgroup_root->nr_cgrps.
    Refreshed on top of cgroup/for-v4.13 which dropped on
    css_set_populated() -> nr_tasks conversion.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup-defs.h |  3 +++
 kernel/cgroup/cgroup-v1.c   |  6 +-----
 kernel/cgroup/cgroup.c      | 10 ++++++++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index ec47101cb1bf..3bc4196bf217 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -166,6 +166,9 @@ struct css_set {
 	/* the default cgroup associated with this css_set */
 	struct cgroup *dfl_cgrp;
 
+	/* internal task count, protected by css_set_lock */
+	int nr_tasks;
+
 	/*
 	 * Lists running through all tasks using this cgroup group.
 	 * mg_tasks lists tasks which belong to this cset but are in the
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 85d75152402d..e9ea5f201fac 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -334,10 +334,6 @@ static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
 /**
  * cgroup_task_count - count the number of tasks in a cgroup.
  * @cgrp: the cgroup in question
- *
- * Return the number of tasks in the cgroup.  The returned number can be
- * higher than the actual number of tasks due to css_set references from
- * namespace roots and temporary usages.
  */
 static int cgroup_task_count(const struct cgroup *cgrp)
 {
@@ -346,7 +342,7 @@ static int cgroup_task_count(const struct cgroup *cgrp)
 
 	spin_lock_irq(&css_set_lock);
 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
-		count += refcount_read(&link->cset->refcount);
+		count += link->cset->nr_tasks;
 	spin_unlock_irq(&css_set_lock);
 	return count;
 }
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8d4e85eae42c..dbfd7028b1c6 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -573,6 +573,11 @@ static int css_set_count	= 1;	/* 1 for init_css_set */
 /**
  * css_set_populated - does a css_set contain any tasks?
  * @cset: target css_set
+ *
+ * css_set_populated() should be the same as !!cset->nr_tasks at steady
+ * state. However, css_set_populated() can be called while a task is being
+ * added to or removed from the linked list before the nr_tasks is
+ * properly updated. Hence, we can't just look at ->nr_tasks here.
  */
 static bool css_set_populated(struct css_set *cset)
 {
@@ -1598,6 +1603,7 @@ static void cgroup_enable_task_cg_lists(void)
 				css_set_update_populated(cset, true);
 			list_add_tail(&p->cg_list, &cset->tasks);
 			get_css_set(cset);
+			cset->nr_tasks++;
 		}
 		spin_unlock(&p->sighand->siglock);
 	} while_each_thread(g, p);
@@ -2064,8 +2070,10 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
 			struct css_set *to_cset = cset->mg_dst_cset;
 
 			get_css_set(to_cset);
+			to_cset->nr_tasks++;
 			css_set_move_task(task, from_cset, to_cset, true);
 			put_css_set_locked(from_cset);
+			from_cset->nr_tasks--;
 		}
 	}
 	spin_unlock_irq(&css_set_lock);
@@ -4789,6 +4797,7 @@ void cgroup_post_fork(struct task_struct *child)
 		cset = task_css_set(current);
 		if (list_empty(&child->cg_list)) {
 			get_css_set(cset);
+			cset->nr_tasks++;
 			css_set_move_task(child, NULL, cset, false);
 		}
 		spin_unlock_irq(&css_set_lock);
@@ -4838,6 +4847,7 @@ void cgroup_exit(struct task_struct *tsk)
 	if (!list_empty(&tsk->cg_list)) {
 		spin_lock_irq(&css_set_lock);
 		css_set_move_task(tsk, cset, NULL, false);
+		cset->nr_tasks--;
 		spin_unlock_irq(&css_set_lock);
 	} else {
 		get_css_set(cset);
-- 
2.13.0

[PATCH 2/7] cgroup: Move debug cgroup to its own file

[Tejun Heo]

From: Waiman Long <longman@redhat.com>

The debug cgroup currently resides within cgroup-v1.c and is enabled
only for v1 cgroup. To enable the debug cgroup also for v2, it makes
sense to put the code into its own file as it will no longer be v1
specific. There is no change to the debug cgroup specific code.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup/Makefile          |   1 +
 kernel/cgroup/cgroup-internal.h |   2 +
 kernel/cgroup/cgroup-v1.c       | 149 +-------------------------------------
 kernel/cgroup/debug.c           | 153 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 157 insertions(+), 148 deletions(-)
 create mode 100644 kernel/cgroup/debug.c

diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile
index 387348a40c64..ce693ccb8c58 100644
--- a/kernel/cgroup/Makefile
+++ b/kernel/cgroup/Makefile
@@ -4,3 +4,4 @@ obj-$(CONFIG_CGROUP_FREEZER) += freezer.o
 obj-$(CONFIG_CGROUP_PIDS) += pids.o
 obj-$(CONFIG_CGROUP_RDMA) += rdma.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
+obj-$(CONFIG_CGROUP_DEBUG) += debug.o
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 00f4d6bf048f..793565c05742 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -192,6 +192,8 @@ int cgroup_rmdir(struct kernfs_node *kn);
 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
 		     struct kernfs_root *kf_root);
 
+int cgroup_task_count(const struct cgroup *cgrp);
+
 /*
  * namespace.c
  */
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index e9ea5f201fac..7bf4b1533f34 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -335,7 +335,7 @@ static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
  * cgroup_task_count - count the number of tasks in a cgroup.
  * @cgrp: the cgroup in question
  */
-static int cgroup_task_count(const struct cgroup *cgrp)
+int cgroup_task_count(const struct cgroup *cgrp)
 {
 	int count = 0;
 	struct cgrp_cset_link *link;
@@ -1259,150 +1259,3 @@ static int __init cgroup_no_v1(char *str)
 	return 1;
 }
 __setup("cgroup_no_v1=", cgroup_no_v1);
-
-
-#ifdef CONFIG_CGROUP_DEBUG
-static struct cgroup_subsys_state *
-debug_css_alloc(struct cgroup_subsys_state *parent_css)
-{
-	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
-
-	if (!css)
-		return ERR_PTR(-ENOMEM);
-
-	return css;
-}
-
-static void debug_css_free(struct cgroup_subsys_state *css)
-{
-	kfree(css);
-}
-
-static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
-				struct cftype *cft)
-{
-	return cgroup_task_count(css->cgroup);
-}
-
-static u64 current_css_set_read(struct cgroup_subsys_state *css,
-				struct cftype *cft)
-{
-	return (u64)(unsigned long)current->cgroups;
-}
-
-static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
-					 struct cftype *cft)
-{
-	u64 count;
-
-	rcu_read_lock();
-	count = refcount_read(&task_css_set(current)->refcount);
-	rcu_read_unlock();
-	return count;
-}
-
-static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
-{
-	struct cgrp_cset_link *link;
-	struct css_set *cset;
-	char *name_buf;
-
-	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
-	if (!name_buf)
-		return -ENOMEM;
-
-	spin_lock_irq(&css_set_lock);
-	rcu_read_lock();
-	cset = rcu_dereference(current->cgroups);
-	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
-		struct cgroup *c = link->cgrp;
-
-		cgroup_name(c, name_buf, NAME_MAX + 1);
-		seq_printf(seq, "Root %d group %s\n",
-			   c->root->hierarchy_id, name_buf);
-	}
-	rcu_read_unlock();
-	spin_unlock_irq(&css_set_lock);
-	kfree(name_buf);
-	return 0;
-}
-
-#define MAX_TASKS_SHOWN_PER_CSS 25
-static int cgroup_css_links_read(struct seq_file *seq, void *v)
-{
-	struct cgroup_subsys_state *css = seq_css(seq);
-	struct cgrp_cset_link *link;
-
-	spin_lock_irq(&css_set_lock);
-	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
-		struct css_set *cset = link->cset;
-		struct task_struct *task;
-		int count = 0;
-
-		seq_printf(seq, "css_set %pK\n", cset);
-
-		list_for_each_entry(task, &cset->tasks, cg_list) {
-			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
-				goto overflow;
-			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
-		}
-
-		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
-			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
-				goto overflow;
-			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
-		}
-		continue;
-	overflow:
-		seq_puts(seq, "  ...\n");
-	}
-	spin_unlock_irq(&css_set_lock);
-	return 0;
-}
-
-static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
-{
-	return (!cgroup_is_populated(css->cgroup) &&
-		!css_has_online_children(&css->cgroup->self));
-}
-
-static struct cftype debug_files[] =  {
-	{
-		.name = "taskcount",
-		.read_u64 = debug_taskcount_read,
-	},
-
-	{
-		.name = "current_css_set",
-		.read_u64 = current_css_set_read,
-	},
-
-	{
-		.name = "current_css_set_refcount",
-		.read_u64 = current_css_set_refcount_read,
-	},
-
-	{
-		.name = "current_css_set_cg_links",
-		.seq_show = current_css_set_cg_links_read,
-	},
-
-	{
-		.name = "cgroup_css_links",
-		.seq_show = cgroup_css_links_read,
-	},
-
-	{
-		.name = "releasable",
-		.read_u64 = releasable_read,
-	},
-
-	{ }	/* terminate */
-};
-
-struct cgroup_subsys debug_cgrp_subsys = {
-	.css_alloc = debug_css_alloc,
-	.css_free = debug_css_free,
-	.legacy_cftypes = debug_files,
-};
-#endif /* CONFIG_CGROUP_DEBUG */
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
new file mode 100644
index 000000000000..1c209aa43733
--- /dev/null
+++ b/kernel/cgroup/debug.c
@@ -0,0 +1,153 @@
+#include <linux/ctype.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+#include "cgroup-internal.h"
+
+static struct cgroup_subsys_state *
+debug_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
+
+	if (!css)
+		return ERR_PTR(-ENOMEM);
+
+	return css;
+}
+
+static void debug_css_free(struct cgroup_subsys_state *css)
+{
+	kfree(css);
+}
+
+/*
+ * debug_taskcount_read - return the number of tasks in a cgroup.
+ * @cgrp: the cgroup in question
+ */
+static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
+				struct cftype *cft)
+{
+	return cgroup_task_count(css->cgroup);
+}
+
+static u64 current_css_set_read(struct cgroup_subsys_state *css,
+				struct cftype *cft)
+{
+	return (u64)(unsigned long)current->cgroups;
+}
+
+static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
+					 struct cftype *cft)
+{
+	u64 count;
+
+	rcu_read_lock();
+	count = refcount_read(&task_css_set(current)->refcount);
+	rcu_read_unlock();
+	return count;
+}
+
+static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
+{
+	struct cgrp_cset_link *link;
+	struct css_set *cset;
+	char *name_buf;
+
+	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+	if (!name_buf)
+		return -ENOMEM;
+
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	cset = rcu_dereference(current->cgroups);
+	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+		struct cgroup *c = link->cgrp;
+
+		cgroup_name(c, name_buf, NAME_MAX + 1);
+		seq_printf(seq, "Root %d group %s\n",
+			   c->root->hierarchy_id, name_buf);
+	}
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+	kfree(name_buf);
+	return 0;
+}
+
+#define MAX_TASKS_SHOWN_PER_CSS 25
+static int cgroup_css_links_read(struct seq_file *seq, void *v)
+{
+	struct cgroup_subsys_state *css = seq_css(seq);
+	struct cgrp_cset_link *link;
+
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
+		struct css_set *cset = link->cset;
+		struct task_struct *task;
+		int count = 0;
+
+		seq_printf(seq, "css_set %pK\n", cset);
+
+		list_for_each_entry(task, &cset->tasks, cg_list) {
+			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
+				goto overflow;
+			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
+		}
+
+		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
+			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
+				goto overflow;
+			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
+		}
+		continue;
+	overflow:
+		seq_puts(seq, "  ...\n");
+	}
+	spin_unlock_irq(&css_set_lock);
+	return 0;
+}
+
+static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	return (!cgroup_is_populated(css->cgroup) &&
+		!css_has_online_children(&css->cgroup->self));
+}
+
+static struct cftype debug_files[] =  {
+	{
+		.name = "taskcount",
+		.read_u64 = debug_taskcount_read,
+	},
+
+	{
+		.name = "current_css_set",
+		.read_u64 = current_css_set_read,
+	},
+
+	{
+		.name = "current_css_set_refcount",
+		.read_u64 = current_css_set_refcount_read,
+	},
+
+	{
+		.name = "current_css_set_cg_links",
+		.seq_show = current_css_set_cg_links_read,
+	},
+
+	{
+		.name = "cgroup_css_links",
+		.seq_show = cgroup_css_links_read,
+	},
+
+	{
+		.name = "releasable",
+		.read_u64 = releasable_read,
+	},
+
+	{ }	/* terminate */
+};
+
+struct cgroup_subsys debug_cgrp_subsys = {
+	.css_alloc = debug_css_alloc,
+	.css_free = debug_css_free,
+	.legacy_cftypes = debug_files,
+};
-- 
2.13.0

[PATCH 3/7] cgroup: Make Kconfig prompt of debug cgroup more accurate

[Tejun Heo]

From: Waiman Long <longman@redhat.com>

The Kconfig prompt and description of the debug cgroup controller
more accurate by saying that it is for debug purpose only and its
interfaces are unstable.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 init/Kconfig          | 7 +++++--
 kernel/cgroup/debug.c | 6 ++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 1d3475fc9496..5f9d13929ae0 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1205,11 +1205,14 @@ config CGROUP_BPF
 	  inet sockets.
 
 config CGROUP_DEBUG
-	bool "Example controller"
+	bool "Debug controller"
 	default n
+	depends on DEBUG_KERNEL
 	help
 	  This option enables a simple controller that exports
-	  debugging information about the cgroups framework.
+	  debugging information about the cgroups framework. This
+	  controller is for control cgroup debugging only. Its
+	  interfaces are not stable.
 
 	  Say N.
 
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 1c209aa43733..cbe77a2087c5 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -1,3 +1,9 @@
+/*
+ * Debug controller
+ *
+ * WARNING: This controller is for cgroup core debugging only.
+ * Its interfaces are unstable and subject to changes at any time.
+ */
 #include <linux/ctype.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
-- 
2.13.0

[PATCH 4/7] cgroup: Make debug cgroup support v2 and thread mode

[Tejun Heo]

From: Waiman Long <longman@redhat.com>

Besides supporting cgroup v2 and thread mode, the following changes
are also made:
 1) current_* cgroup files now resides only at the root as we don't
    need duplicated files of the same function all over the cgroup
    hierarchy.
 2) The cgroup_css_links_read() function is modified to report
    the number of tasks that are skipped because of overflow.
 3) The number of extra unaccounted references are displayed.
 4) The current_css_set_read() function now prints out the addresses of
    the css'es associated with the current css_set.
 5) A new cgroup_subsys_states file is added to display the css objects
    associated with a cgroup.
 6) A new cgroup_masks file is added to display the various controller
    bit masks in the cgroup.

tj: Dropped thread mode related information for now so that debug
    controller changes aren't blocked on the thread mode.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup/debug.c | 170 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 153 insertions(+), 17 deletions(-)

diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index cbe77a2087c5..057d9b07f461 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -36,10 +36,37 @@ static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
 	return cgroup_task_count(css->cgroup);
 }
 
-static u64 current_css_set_read(struct cgroup_subsys_state *css,
-				struct cftype *cft)
+static int current_css_set_read(struct seq_file *seq, void *v)
 {
-	return (u64)(unsigned long)current->cgroups;
+	struct css_set *cset;
+	struct cgroup_subsys *ss;
+	struct cgroup_subsys_state *css;
+	int i, refcnt;
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	cset = rcu_dereference(current->cgroups);
+	refcnt = refcount_read(&cset->refcount);
+	seq_printf(seq, "css_set %pK %d", cset, refcnt);
+	if (refcnt > cset->nr_tasks)
+		seq_printf(seq, " +%d", refcnt - cset->nr_tasks);
+	seq_puts(seq, "\n");
+
+	/*
+	 * Print the css'es stored in the current css_set.
+	 */
+	for_each_subsys(ss, i) {
+		css = cset->subsys[ss->id];
+		if (!css)
+			continue;
+		seq_printf(seq, "%2d: %-4s\t- %lx[%d]\n", ss->id, ss->name,
+			  (unsigned long)css, css->id);
+	}
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+	return 0;
 }
 
 static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
@@ -84,31 +111,126 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
 {
 	struct cgroup_subsys_state *css = seq_css(seq);
 	struct cgrp_cset_link *link;
+	int dead_cnt = 0, extra_refs = 0;
 
 	spin_lock_irq(&css_set_lock);
 	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
 		struct css_set *cset = link->cset;
 		struct task_struct *task;
 		int count = 0;
+		int refcnt = refcount_read(&cset->refcount);
 
-		seq_printf(seq, "css_set %pK\n", cset);
+		seq_printf(seq, " %d", refcnt);
+		if (refcnt - cset->nr_tasks > 0) {
+			int extra = refcnt - cset->nr_tasks;
+
+			seq_printf(seq, " +%d", extra);
+			/*
+			 * Take out the one additional reference in
+			 * init_css_set.
+			 */
+			if (cset == &init_css_set)
+				extra--;
+			extra_refs += extra;
+		}
+		seq_puts(seq, "\n");
 
 		list_for_each_entry(task, &cset->tasks, cg_list) {
-			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
-				goto overflow;
-			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
+			if (count++ <= MAX_TASKS_SHOWN_PER_CSS)
+				seq_printf(seq, "  task %d\n",
+					   task_pid_vnr(task));
 		}
 
 		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
-			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
-				goto overflow;
-			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
+			if (count++ <= MAX_TASKS_SHOWN_PER_CSS)
+				seq_printf(seq, "  task %d\n",
+					   task_pid_vnr(task));
 		}
-		continue;
-	overflow:
-		seq_puts(seq, "  ...\n");
+		/* show # of overflowed tasks */
+		if (count > MAX_TASKS_SHOWN_PER_CSS)
+			seq_printf(seq, "  ... (%d)\n",
+				   count - MAX_TASKS_SHOWN_PER_CSS);
+
+		if (cset->dead) {
+			seq_puts(seq, "    [dead]\n");
+			dead_cnt++;
+		}
+
+		WARN_ON(count != cset->nr_tasks);
 	}
 	spin_unlock_irq(&css_set_lock);
+
+	if (!dead_cnt && !extra_refs)
+		return 0;
+
+	seq_puts(seq, "\n");
+	if (extra_refs)
+		seq_printf(seq, "extra references = %d\n", extra_refs);
+	if (dead_cnt)
+		seq_printf(seq, "dead css_sets = %d\n", dead_cnt);
+
+	return 0;
+}
+
+static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	struct cgroup_subsys *ss;
+	struct cgroup_subsys_state *css;
+	char pbuf[16];
+	int i;
+
+	mutex_lock(&cgroup_mutex);
+	for_each_subsys(ss, i) {
+		css = rcu_dereference_check(cgrp->subsys[ss->id], true);
+		if (!css)
+			continue;
+
+		pbuf[0] = '\0';
+
+		/* Show the parent CSS if applicable*/
+		if (css->parent)
+			snprintf(pbuf, sizeof(pbuf) - 1, " P=%d",
+				 css->parent->id);
+		seq_printf(seq, "%2d: %-4s\t- %lx[%d] %d%s\n", ss->id, ss->name,
+			  (unsigned long)css, css->id,
+			  atomic_read(&css->online_cnt), pbuf);
+	}
+	mutex_unlock(&cgroup_mutex);
+	return 0;
+}
+
+static int cgroup_masks_read(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	struct cgroup_subsys *ss;
+	int i, j;
+	struct {
+		u16  *mask;
+		char *name;
+	} mask_list[] = {
+		{ &cgrp->subtree_control,  "subtree_control"  },
+		{ &cgrp->subtree_ss_mask,  "subtree_ss_mask"  },
+	};
+
+	mutex_lock(&cgroup_mutex);
+	for (i = 0; i < ARRAY_SIZE(mask_list); i++) {
+		u16 mask = *mask_list[i].mask;
+		bool first = true;
+
+		seq_printf(seq, "%-17s: ", mask_list[i].name);
+		for_each_subsys(ss, j) {
+			if (!(mask & (1 << ss->id)))
+				continue;
+			if (!first)
+				seq_puts(seq, ", ");
+			seq_puts(seq, ss->name);
+			first = false;
+		}
+		seq_putc(seq, '\n');
+	}
+
+	mutex_unlock(&cgroup_mutex);
 	return 0;
 }
 
@@ -126,17 +248,20 @@ static struct cftype debug_files[] =  {
 
 	{
 		.name = "current_css_set",
-		.read_u64 = current_css_set_read,
+		.seq_show = current_css_set_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
 	},
 
 	{
 		.name = "current_css_set_refcount",
 		.read_u64 = current_css_set_refcount_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
 	},
 
 	{
 		.name = "current_css_set_cg_links",
 		.seq_show = current_css_set_cg_links_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
 	},
 
 	{
@@ -145,6 +270,16 @@ static struct cftype debug_files[] =  {
 	},
 
 	{
+		.name = "cgroup_subsys_states",
+		.seq_show = cgroup_subsys_states_read,
+	},
+
+	{
+		.name = "cgroup_masks",
+		.seq_show = cgroup_masks_read,
+	},
+
+	{
 		.name = "releasable",
 		.read_u64 = releasable_read,
 	},
@@ -153,7 +288,8 @@ static struct cftype debug_files[] =  {
 };
 
 struct cgroup_subsys debug_cgrp_subsys = {
-	.css_alloc = debug_css_alloc,
-	.css_free = debug_css_free,
-	.legacy_cftypes = debug_files,
+	.css_alloc	= debug_css_alloc,
+	.css_free	= debug_css_free,
+	.legacy_cftypes	= debug_files,
+	.dfl_cftypes	= debug_files,
 };
-- 
2.13.0

[PATCH 5/7] cgroup: make debug an implicit controller on cgroup2

[Tejun Heo]

Make debug an implicit controller on cgroup2 which is enabled by
"cgroup_debug" boot param.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/debug.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 057d9b07f461..d61e692a5338 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -240,7 +240,7 @@ static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
 		!css_has_online_children(&css->cgroup->self));
 }
 
-static struct cftype debug_files[] =  {
+static struct cftype debug_legacy_files[] =  {
 	{
 		.name = "taskcount",
 		.read_u64 = debug_taskcount_read,
@@ -287,9 +287,62 @@ static struct cftype debug_files[] =  {
 	{ }	/* terminate */
 };
 
+static struct cftype debug_files[] =  {
+	{
+		.name = "taskcount",
+		.read_u64 = debug_taskcount_read,
+	},
+
+	{
+		.name = "current_css_set",
+		.seq_show = current_css_set_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_refcount",
+		.read_u64 = current_css_set_refcount_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_cg_links",
+		.seq_show = current_css_set_cg_links_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "css_links",
+		.seq_show = cgroup_css_links_read,
+	},
+
+	{
+		.name = "csses",
+		.seq_show = cgroup_subsys_states_read,
+	},
+
+	{
+		.name = "masks",
+		.seq_show = cgroup_masks_read,
+	},
+
+	{ }	/* terminate */
+};
+
 struct cgroup_subsys debug_cgrp_subsys = {
 	.css_alloc	= debug_css_alloc,
 	.css_free	= debug_css_free,
-	.legacy_cftypes	= debug_files,
-	.dfl_cftypes	= debug_files,
+	.legacy_cftypes	= debug_legacy_files,
 };
+
+/*
+ * On v2, debug is an implicit controller enabled by "cgroup_debug" boot
+ * parameter.
+ */
+static int __init enable_cgroup_debug(char *str)
+{
+	debug_cgrp_subsys.dfl_cftypes = debug_files;
+	debug_cgrp_subsys.implicit_on_dfl = true;
+	return 1;
+}
+__setup("cgroup_debug", enable_cgroup_debug);
-- 
2.13.0

[PATCH 6/7] cgroup: refactor cgroup_masks_read() in the debug controller

[Tejun Heo]

Factor out cgroup_masks_read_one() out of cgroup_masks_read() for
simplicity.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/debug.c | 46 +++++++++++++++++++++-------------------------
 1 file changed, 21 insertions(+), 25 deletions(-)

diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index d61e692a5338..163fdbd7adf6 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -200,36 +200,32 @@ static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
 	return 0;
 }
 
-static int cgroup_masks_read(struct seq_file *seq, void *v)
+static void cgroup_masks_read_one(struct seq_file *seq, const char *name,
+				  u16 mask)
 {
-	struct cgroup *cgrp = seq_css(seq)->cgroup;
 	struct cgroup_subsys *ss;
-	int i, j;
-	struct {
-		u16  *mask;
-		char *name;
-	} mask_list[] = {
-		{ &cgrp->subtree_control,  "subtree_control"  },
-		{ &cgrp->subtree_ss_mask,  "subtree_ss_mask"  },
-	};
+	int ssid;
+	bool first = true;
 
-	mutex_lock(&cgroup_mutex);
-	for (i = 0; i < ARRAY_SIZE(mask_list); i++) {
-		u16 mask = *mask_list[i].mask;
-		bool first = true;
-
-		seq_printf(seq, "%-17s: ", mask_list[i].name);
-		for_each_subsys(ss, j) {
-			if (!(mask & (1 << ss->id)))
-				continue;
-			if (!first)
-				seq_puts(seq, ", ");
-			seq_puts(seq, ss->name);
-			first = false;
-		}
-		seq_putc(seq, '\n');
+	seq_printf(seq, "%-17s: ", name);
+	for_each_subsys(ss, ssid) {
+		if (!(mask & (1 << ssid)))
+			continue;
+		if (!first)
+			seq_puts(seq, ", ");
+		seq_puts(seq, ss->name);
+		first = false;
 	}
+	seq_putc(seq, '\n');
+}
 
+static int cgroup_masks_read(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	mutex_lock(&cgroup_mutex);
+	cgroup_masks_read_one(seq, "subtree_control", cgrp->subtree_control);
+	cgroup_masks_read_one(seq, "subtree_ss_mask", cgrp->subtree_ss_mask);
 	mutex_unlock(&cgroup_mutex);
 	return 0;
 }
-- 
2.13.0

[PATCH 7/7] cgroup: fix lockdep warning in debug controller

[Tejun Heo]

The debug controller grabs cgroup_mutex from interface file show
functions which can deadlock and triggers lockdep warnings.  Fix it by
using cgroup_kn_lock_live()/cgroup_kn_unlock() instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/debug.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 163fdbd7adf6..dac46af22782 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -38,12 +38,15 @@ static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
 
 static int current_css_set_read(struct seq_file *seq, void *v)
 {
+	struct kernfs_open_file *of = seq->private;
 	struct css_set *cset;
 	struct cgroup_subsys *ss;
 	struct cgroup_subsys_state *css;
 	int i, refcnt;
 
-	mutex_lock(&cgroup_mutex);
+	if (!cgroup_kn_lock_live(of->kn, false))
+		return -ENODEV;
+
 	spin_lock_irq(&css_set_lock);
 	rcu_read_lock();
 	cset = rcu_dereference(current->cgroups);
@@ -65,7 +68,7 @@ static int current_css_set_read(struct seq_file *seq, void *v)
 	}
 	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
-	mutex_unlock(&cgroup_mutex);
+	cgroup_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -174,13 +177,17 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
 
 static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
 {
-	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	struct kernfs_open_file *of = seq->private;
+	struct cgroup *cgrp;
 	struct cgroup_subsys *ss;
 	struct cgroup_subsys_state *css;
 	char pbuf[16];
 	int i;
 
-	mutex_lock(&cgroup_mutex);
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
+
 	for_each_subsys(ss, i) {
 		css = rcu_dereference_check(cgrp->subsys[ss->id], true);
 		if (!css)
@@ -196,7 +203,8 @@ static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
 			  (unsigned long)css, css->id,
 			  atomic_read(&css->online_cnt), pbuf);
 	}
-	mutex_unlock(&cgroup_mutex);
+
+	cgroup_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -221,12 +229,17 @@ static void cgroup_masks_read_one(struct seq_file *seq, const char *name,
 
 static int cgroup_masks_read(struct seq_file *seq, void *v)
 {
-	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	struct kernfs_open_file *of = seq->private;
+	struct cgroup *cgrp;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
 
-	mutex_lock(&cgroup_mutex);
 	cgroup_masks_read_one(seq, "subtree_control", cgrp->subtree_control);
 	cgroup_masks_read_one(seq, "subtree_ss_mask", cgrp->subtree_ss_mask);
-	mutex_unlock(&cgroup_mutex);
+
+	cgroup_kn_unlock(of->kn);
 	return 0;
 }
 
-- 
2.13.0

Re: [PATCHSET] cgroup: Make debug controller useful for debugging

[Waiman Long]

On 06/14/2017 04:08 PM, Tejun Heo wrote:
> Hello, Waiman.
>
> I dropped the thread mode part of the patches so that these aren't
> blocked on thread mode, made the debug controller an implicit one on
> cgroup2 which is enabled by "cgroup_debug" boot param (we can't mask
> it on cgroup1 with the boot param at this point), and fixed the
> lockdep warnings.
>
> I applied the updated patches + follow up changes to cgroup/for-4.13.
>
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-4.13
>
> I'd really appreciate if you can go over the patches and check that I
> didn't do anything stupid.
>
> Thanks.
>
> --
> tejun

Thanks for fixing issues in my debug controller patchset. I am fine with
the changes.

Acked-by: Waiman Long <longman@redhat.com>

-Longman