cgroup: add tracepoints for basic operations

Debugging what goes wrong with cgroup setup can get hairy.  Add
tracepoints for cgroup hierarchy mount, cgroup creation/destruction
and task migration operations for better visibility.

Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 188 insertions, 0 deletions

diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
new file mode 100644
index 000000000000..ab68640a18d0
--- /dev/null
+++ b/include/trace/events/cgroup.h
@@ -0,0 +1,163 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM cgroup
+
+#if !defined(_TRACE_CGROUP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_CGROUP_H
+
+#include <linux/cgroup.h>
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(cgroup_root,
+
+        TP_PROTO(struct cgroup_root *root),
+
+        TP_ARGS(root),
+
+        TP_STRUCT__entry(
+                __field(        int,            root                    )
+                __field(        u16,            ss_mask                 )
+                __string(       name,           root->name              )
+        ),
+
+        TP_fast_assign(
+                __entry->root = root->hierarchy_id;
+                __entry->ss_mask = root->subsys_mask;
+                __assign_str(name, root->name);
+        ),
+
+        TP_printk("root=%d ss_mask=%#x name=%s",
+                  __entry->root, __entry->ss_mask, __get_str(name))
+);
+
+DEFINE_EVENT(cgroup_root, cgroup_setup_root,
+
+        TP_PROTO(struct cgroup_root *root),
+
+        TP_ARGS(root)
+);
+
+DEFINE_EVENT(cgroup_root, cgroup_destroy_root,
+
+        TP_PROTO(struct cgroup_root *root),
+
+        TP_ARGS(root)
+);
+
+DEFINE_EVENT(cgroup_root, cgroup_remount,
+
+        TP_PROTO(struct cgroup_root *root),
+
+        TP_ARGS(root)
+);
+
+DECLARE_EVENT_CLASS(cgroup,
+
+        TP_PROTO(struct cgroup *cgrp),
+
+        TP_ARGS(cgrp),
+
+        TP_STRUCT__entry(
+                __field(        int,            root                    )
+                __field(        int,            id                      )
+                __field(        int,            level                   )
+                __dynamic_array(char,           path,
+                                cgrp->kn ? cgroup_path(cgrp, NULL, 0) + 1
+                                         : strlen("(null)"))
+        ),
+
+        TP_fast_assign(
+                __entry->root = cgrp->root->hierarchy_id;
+                __entry->id = cgrp->id;
+                __entry->level = cgrp->level;
+                if (cgrp->kn)
+                        cgroup_path(cgrp, __get_dynamic_array(path),
+                                    __get_dynamic_array_len(path));
+                else
+                        __assign_str(path, "(null)");
+        ),
+
+        TP_printk("root=%d id=%d level=%d path=%s",
+                  __entry->root, __entry->id, __entry->level, __get_str(path))
+);
+
+DEFINE_EVENT(cgroup, cgroup_mkdir,
+
+        TP_PROTO(struct cgroup *cgroup),
+
+        TP_ARGS(cgroup)
+);
+
+DEFINE_EVENT(cgroup, cgroup_rmdir,
+
+        TP_PROTO(struct cgroup *cgroup),
+
+        TP_ARGS(cgroup)
+);
+
+DEFINE_EVENT(cgroup, cgroup_release,
+
+        TP_PROTO(struct cgroup *cgroup),
+
+        TP_ARGS(cgroup)
+);
+
+DEFINE_EVENT(cgroup, cgroup_rename,
+
+        TP_PROTO(struct cgroup *cgroup),
+
+        TP_ARGS(cgroup)
+);
+
+DECLARE_EVENT_CLASS(cgroup_migrate,
+
+        TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+
+        TP_ARGS(dst_cgrp, task, threadgroup),
+
+        TP_STRUCT__entry(
+                __field(        int,            dst_root                )
+                __field(        int,            dst_id                  )
+                __field(        int,            dst_level               )
+                __dynamic_array(char,           dst_path,
+                                dst_cgrp->kn ? cgroup_path(dst_cgrp, NULL, 0) + 1
+                                             : strlen("(null)"))
+                __field(        int,            pid                     )
+                __string(       comm,           task->comm              )
+        ),
+
+        TP_fast_assign(
+                __entry->dst_root = dst_cgrp->root->hierarchy_id;
+                __entry->dst_id = dst_cgrp->id;
+                __entry->dst_level = dst_cgrp->level;
+                if (dst_cgrp->kn)
+                        cgroup_path(dst_cgrp, __get_dynamic_array(dst_path),
+                                    __get_dynamic_array_len(dst_path));
+                else
+                        __assign_str(dst_path, "(null)");
+                __entry->pid = task->pid;
+                __assign_str(comm, task->comm);
+        ),
+
+        TP_printk("dst_root=%d dst_id=%d dst_level=%d dst_path=%s pid=%d comm=%s",
+                  __entry->dst_root, __entry->dst_id, __entry->dst_level,
+                  __get_str(dst_path), __entry->pid, __get_str(comm))
+);
+
+DEFINE_EVENT(cgroup_migrate, cgroup_attach_task,
+
+        TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+
+        TP_ARGS(dst_cgrp, task, threadgroup)
+);
+
+DEFINE_EVENT(cgroup_migrate, cgroup_transfer_tasks,
+
+        TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+
+        TP_ARGS(dst_cgrp, task, threadgroup)
+);
+
+#endif /* _TRACE_CGROUP_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3861161e460f..5e2e81ad9175 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -64,6 +64,9 @@
 #include <linux/file.h>
 #include <net/sock.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/cgroup.h>
+
 /*
  * pidlists linger the following amount before being destroyed.  The goal
  * is avoiding frequent destruction in the middle of consecutive read calls
@@ -1176,6 +1179,8 @@ static void cgroup_destroy_root(struct cgroup_root *root)
         struct cgroup *cgrp = &root->cgrp;
         struct cgrp_cset_link *link, *tmp_link;
 
+        trace_cgroup_destroy_root(root);
+
         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
 
         BUG_ON(atomic_read(&root->nr_cgrps));
@@ -1874,6 +1879,9 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
                 strcpy(root->release_agent_path, opts.release_agent);
                 spin_unlock(&release_agent_path_lock);
         }
+
+        trace_cgroup_remount(root);
+
  out_unlock:
         kfree(opts.release_agent);
         kfree(opts.name);
@@ -2031,6 +2039,8 @@ static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
         if (ret)
                 goto destroy_root;
 
+        trace_cgroup_setup_root(root);
+
         /*
          * There must be no failure case after here, since rebinding takes
          * care of subsystems' refcounts, which are explicitly dropped in
@@ -2825,6 +2835,10 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
                 ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
 
         cgroup_migrate_finish(&preloaded_csets);
+
+        if (!ret)
+                trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
+
         return ret;
 }
 
@@ -3587,6 +3601,8 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
         mutex_lock(&cgroup_mutex);
 
         ret = kernfs_rename(kn, new_parent, new_name_str);
+        if (!ret)
+                trace_cgroup_rename(cgrp);
 
         mutex_unlock(&cgroup_mutex);
 
@@ -4355,6 +4371,8 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 
                 if (task) {
                         ret = cgroup_migrate(task, false, to->root);
+                        if (!ret)
+                                trace_cgroup_transfer_tasks(to, task, false);
                         put_task_struct(task);
                 }
         } while (task && !ret);
@@ -5020,6 +5038,8 @@ static void css_release_work_fn(struct work_struct *work)
                         ss->css_released(css);
         } else {
                 /* cgroup release path */
+                trace_cgroup_release(cgrp);
+
                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
                 cgrp->id = -1;
 
@@ -5306,6 +5326,8 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
         if (ret)
                 goto out_destroy;
 
+        trace_cgroup_mkdir(cgrp);
+
         /* let's create and online css's */
         kernfs_activate(kn);
 
@@ -5481,6 +5503,9 @@ static int cgroup_rmdir(struct kernfs_node *kn)
 
         ret = cgroup_destroy_locked(cgrp);
 
+        if (!ret)
+                trace_cgroup_rmdir(cgrp);
+
         cgroup_kn_unlock(kn);
         return ret;
 }