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Subject[RFC PATCH 09/14] cgroup: Make debug cgroup support v2 and thread mode
Date
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 relationship between proc_cset and threaded_csets are displayed.
4) The number of extra unaccounted references are displayed.
5) The status of being a thread root or threaded cgroup is displayed.
6) The current_css_set_read() function now prints out the addresses of
the css'es associated with the current css_set.
7) A new cgroup_subsys_states file is added to display the css objects
associated with a cgroup.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/debug.c | 151 ++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 134 insertions(+), 17 deletions(-)

diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index c8f7590..4d74458 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -38,10 +38,37 @@ static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
return count;
}

-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 = atomic_read(&cset->refcount);
+ seq_printf(seq, "css_set %pK %d", cset, refcnt);
+ if (refcnt > cset->task_count)
+ seq_printf(seq, " +%d", refcnt - cset->task_count);
+ 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,
@@ -86,31 +113,111 @@ 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, threaded_csets = 0;

spin_lock_irq(&css_set_lock);
+ if (css->cgroup->proc_cgrp)
+ seq_puts(seq, (css->cgroup->proc_cgrp == css->cgroup)
+ ? "[thread root]\n" : "[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 = atomic_read(&cset->refcount);

- seq_printf(seq, "css_set %pK\n", cset);
+ /*
+ * 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 (cset->proc_cset != cset) {
+ threaded_csets++;
+ seq_printf(seq, "=>%pK", cset->proc_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->task_count > 0) {
+ int extra = refcnt - cset->task_count;
+
+ 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->task_count);
}
spin_unlock_irq(&css_set_lock);
+
+ 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)
+ 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;
+ int i;
+
+ mutex_lock(&cgroup_mutex);
+ for_each_subsys(ss, i) {
+ css = rcu_dereference_check(cgrp->subsys[ss->id], true);
+ if (!css)
+ continue;
+ seq_printf(seq, "%2d: %-4s\t- %lx[%d] %d\n", ss->id, ss->name,
+ (unsigned long)css, css->id,
+ atomic_read(&css->online_cnt));
+ }
+ mutex_unlock(&cgroup_mutex);
return 0;
}

@@ -128,17 +235,20 @@ static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)

{
.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,
},

{
@@ -147,6 +257,11 @@ static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
},

{
+ .name = "cgroup_subsys_states",
+ .seq_show = cgroup_subsys_states_read,
+ },
+
+ {
.name = "releasable",
.read_u64 = releasable_read,
},
@@ -155,7 +270,9 @@ static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
};

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,
+ .threaded = true,
};
--
1.8.3.1
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