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

Tejun Heo
2017-06-14T20:09:01Z

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