[PATCH 6/6] cgroup: update debug controller to print out thread mode information

Tejun Heo
2017-07-17T02:08:02Z

From: Waiman Long <longman@redhat.com>

Update debug controller so that it prints out debug info about thread
mode.

1) The relationship between proc_cset and threaded_csets are displayed.
2) The status of being a thread root or threaded cgroup is displayed.

This patch is extracted from Waiman's larger patch.

Patch-originally-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/cgroup/cgroup-internal.h | 2 ++
kernel/cgroup/cgroup.c | 4 +--
kernel/cgroup/debug.c | 58 +++++++++++++++++++++++++++++++----------
3 files changed, 48 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index f10eb19..c167a40 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -153,6 +153,8 @@ static inline void get_css_set(struct css_set *cset)

bool cgroup_ssid_enabled(int ssid);
bool cgroup_on_dfl(const struct cgroup *cgrp);
+bool cgroup_is_thread_root(struct cgroup *cgrp);
+bool cgroup_is_threaded(struct cgroup *cgrp);

struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root);
struct cgroup *task_cgroup_from_root(struct task_struct *task,
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 7097ce4..2f34020 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -333,7 +333,7 @@ static bool cgroup_has_tasks(struct cgroup *cgrp)
return cgrp->nr_populated_csets;
}

-static bool cgroup_is_threaded(struct cgroup *cgrp)
+bool cgroup_is_threaded(struct cgroup *cgrp)
{
return cgrp->dom_cgrp != cgrp;
}
@@ -372,7 +372,7 @@ static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
}

/* is @cgrp root of a threaded subtree? */
-static bool cgroup_is_thread_root(struct cgroup *cgrp)
+bool cgroup_is_thread_root(struct cgroup *cgrp)
{
/* thread root should be a domain */
if (cgroup_is_threaded(cgrp))
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index dac46af..062904f 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -114,27 +114,54 @@ 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;
+ int dead_cnt = 0, extra_refs = 0, threaded_csets = 0;

spin_lock_irq(&css_set_lock);
+
+ if (cgroup_is_thread_root(css->cgroup))
+ seq_puts(seq, "[thread root]\n");
+ else if (cgroup_is_threaded(css->cgroup))
+ seq_puts(seq, "[threaded]\n");
+
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, " %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;
+ /*
+ * Print out the proc_cset and threaded_cset relationship
+ * and highlight difference between refcount and task_count.
+ */
+ seq_printf(seq, "css_set %pK", cset);
+ if (rcu_dereference_protected(cset->dom_cset, 1) != cset) {
+ threaded_csets++;
+ seq_printf(seq, "=>%pK", cset->dom_cset);
+ }
+ if (!list_empty(&cset->threaded_csets)) {
+ struct css_set *tcset;
+ int idx = 0;
+
+ list_for_each_entry(tcset, &cset->threaded_csets,
+ threaded_csets_node) {
+ seq_puts(seq, idx ? "," : "<=");
+ seq_printf(seq, "%pK", tcset);
+ idx++;
+ }
+ } else {
+ 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");

@@ -163,10 +190,12 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
}
spin_unlock_irq(&css_set_lock);

- if (!dead_cnt && !extra_refs)
+ if (!dead_cnt && !extra_refs && !threaded_csets)
return 0;

seq_puts(seq, "\n");
+ if (threaded_csets)
+ seq_printf(seq, "threaded css_sets = %d\n", threaded_csets);
if (extra_refs)
seq_printf(seq, "extra references = %d\n", extra_refs);
if (dead_cnt)
@@ -342,6 +371,7 @@ struct cgroup_subsys debug_cgrp_subsys = {
.css_alloc = debug_css_alloc,
.css_free = debug_css_free,
.legacy_cftypes = debug_legacy_files,
+ .threaded = true,
};

/*
--
2.9.3