Merge branch 'for-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:
 "Just one commit from Steven to take out spin lock from trace event
  handlers"

* 'for-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup/tracing: Move taking of spin lock out of trace event handlers

4 files changed, 58 insertions, 31 deletions

diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
index d74722c2ac8b..a401ff5e7847 100644
--- a/include/trace/events/cgroup.h
+++ b/include/trace/events/cgroup.h
@@ -53,24 +53,22 @@ DEFINE_EVENT(cgroup_root, cgroup_remount,
 
 DECLARE_EVENT_CLASS(cgroup,
 
-	TP_PROTO(struct cgroup *cgrp),
+	TP_PROTO(struct cgroup *cgrp, const char *path),
 
-	TP_ARGS(cgrp),
+	TP_ARGS(cgrp, path),
 
 	TP_STRUCT__entry(
 		__field(	int,		root			)
 		__field(	int,		id			)
 		__field(	int,		level			)
-		__dynamic_array(char,		path,
-				cgroup_path(cgrp, NULL, 0) + 1)
+		__string(	path,		path			)
 	),
 
 	TP_fast_assign(
 		__entry->root = cgrp->root->hierarchy_id;
 		__entry->id = cgrp->id;
 		__entry->level = cgrp->level;
-		cgroup_path(cgrp, __get_dynamic_array(path),
-				  __get_dynamic_array_len(path));
+		__assign_str(path, path);
 	),
 
 	TP_printk("root=%d id=%d level=%d path=%s",
@@ -79,45 +77,45 @@ DECLARE_EVENT_CLASS(cgroup,
 
 DEFINE_EVENT(cgroup, cgroup_mkdir,
 
-	TP_PROTO(struct cgroup *cgroup),
+	TP_PROTO(struct cgroup *cgrp, const char *path),
 
-	TP_ARGS(cgroup)
+	TP_ARGS(cgrp, path)
 );
 
 DEFINE_EVENT(cgroup, cgroup_rmdir,
 
-	TP_PROTO(struct cgroup *cgroup),
+	TP_PROTO(struct cgroup *cgrp, const char *path),
 
-	TP_ARGS(cgroup)
+	TP_ARGS(cgrp, path)
 );
 
 DEFINE_EVENT(cgroup, cgroup_release,
 
-	TP_PROTO(struct cgroup *cgroup),
+	TP_PROTO(struct cgroup *cgrp, const char *path),
 
-	TP_ARGS(cgroup)
+	TP_ARGS(cgrp, path)
 );
 
 DEFINE_EVENT(cgroup, cgroup_rename,
 
-	TP_PROTO(struct cgroup *cgroup),
+	TP_PROTO(struct cgroup *cgrp, const char *path),
 
-	TP_ARGS(cgroup)
+	TP_ARGS(cgrp, path)
 );
 
 DECLARE_EVENT_CLASS(cgroup_migrate,
 
-	TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+	TP_PROTO(struct cgroup *dst_cgrp, const char *path,
+		 struct task_struct *task, bool threadgroup),
 
-	TP_ARGS(dst_cgrp, task, threadgroup),
+	TP_ARGS(dst_cgrp, path, task, threadgroup),
 
 	TP_STRUCT__entry(
 		__field(	int,		dst_root		)
 		__field(	int,		dst_id			)
 		__field(	int,		dst_level		)
-		__dynamic_array(char,		dst_path,
-				cgroup_path(dst_cgrp, NULL, 0) + 1)
 		__field(	int,		pid			)
+		__string(	dst_path,	path			)
 		__string(	comm,		task->comm		)
 	),
 
@@ -125,8 +123,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 		__entry->dst_root = dst_cgrp->root->hierarchy_id;
 		__entry->dst_id = dst_cgrp->id;
 		__entry->dst_level = dst_cgrp->level;
-		cgroup_path(dst_cgrp, __get_dynamic_array(dst_path),
-				      __get_dynamic_array_len(dst_path));
+		__assign_str(dst_path, path);
 		__entry->pid = task->pid;
 		__assign_str(comm, task->comm);
 	),
@@ -138,16 +135,18 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 
 DEFINE_EVENT(cgroup_migrate, cgroup_attach_task,
 
-	TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+	TP_PROTO(struct cgroup *dst_cgrp, const char *path,
+		 struct task_struct *task, bool threadgroup),
 
-	TP_ARGS(dst_cgrp, task, threadgroup)
+	TP_ARGS(dst_cgrp, path, task, threadgroup)
 );
 
 DEFINE_EVENT(cgroup_migrate, cgroup_transfer_tasks,
 
-	TP_PROTO(struct cgroup *dst_cgrp, struct task_struct *task, bool threadgroup),
+	TP_PROTO(struct cgroup *dst_cgrp, const char *path,
+		 struct task_struct *task, bool threadgroup),
 
-	TP_ARGS(dst_cgrp, task, threadgroup)
+	TP_ARGS(dst_cgrp, path, task, threadgroup)
 );
 
 #endif /* _TRACE_CGROUP_H */
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 77ff1cd6a252..75568fcf2180 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -8,6 +8,32 @@
 #include <linux/list.h>
 #include <linux/refcount.h>
 
+#define TRACE_CGROUP_PATH_LEN 1024
+extern spinlock_t trace_cgroup_path_lock;
+extern char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
+
+/*
+ * cgroup_path() takes a spin lock. It is good practice not to take
+ * spin locks within trace point handlers, as they are mostly hidden
+ * from normal view. As cgroup_path() can take the kernfs_rename_lock
+ * spin lock, it is best to not call that function from the trace event
+ * handler.
+ *
+ * Note: trace_cgroup_##type##_enabled() is a static branch that will only
+ *       be set when the trace event is enabled.
+ */
+#define TRACE_CGROUP_PATH(type, cgrp, ...)				\
+	do {								\
+		if (trace_cgroup_##type##_enabled()) {			\
+			spin_lock(&trace_cgroup_path_lock);		\
+			cgroup_path(cgrp, trace_cgroup_path,		\
+				    TRACE_CGROUP_PATH_LEN);		\
+			trace_cgroup_##type(cgrp, trace_cgroup_path,	\
+					    ##__VA_ARGS__);		\
+			spin_unlock(&trace_cgroup_path_lock);		\
+		}							\
+	} while (0)
+
 /*
  * A cgroup can be associated with multiple css_sets as different tasks may
  * belong to different cgroups on different hierarchies.  In the other
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 8b4f0768efd6..51063e7a93c2 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -135,7 +135,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 		if (task) {
 			ret = cgroup_migrate(task, false, &mgctx);
 			if (!ret)
-				trace_cgroup_transfer_tasks(to, task, false);
+				TRACE_CGROUP_PATH(transfer_tasks, to, task, false);
 			put_task_struct(task);
 		}
 	} while (task && !ret);
@@ -865,7 +865,7 @@ static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent
 
 	ret = kernfs_rename(kn, new_parent, new_name_str);
 	if (!ret)
-		trace_cgroup_rename(cgrp);
+		TRACE_CGROUP_PATH(rename, cgrp);
 
 	mutex_unlock(&cgroup_mutex);
 
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 35cf3d71f8aa..aae10baf1902 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -83,6 +83,9 @@ EXPORT_SYMBOL_GPL(cgroup_mutex);
 EXPORT_SYMBOL_GPL(css_set_lock);
 #endif
 
+DEFINE_SPINLOCK(trace_cgroup_path_lock);
+char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
+
 /*
  * Protects cgroup_idr and css_idr so that IDs can be released without
  * grabbing cgroup_mutex.
@@ -2638,7 +2641,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 	cgroup_migrate_finish(&mgctx);
 
 	if (!ret)
-		trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
+		TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
 
 	return ret;
 }
@@ -4636,7 +4639,7 @@ static void css_release_work_fn(struct work_struct *work)
 		struct cgroup *tcgrp;
 
 		/* cgroup release path */
-		trace_cgroup_release(cgrp);
+		TRACE_CGROUP_PATH(release, cgrp);
 
 		if (cgroup_on_dfl(cgrp))
 			cgroup_rstat_flush(cgrp);
@@ -4979,7 +4982,7 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
 	if (ret)
 		goto out_destroy;
 
-	trace_cgroup_mkdir(cgrp);
+	TRACE_CGROUP_PATH(mkdir, cgrp);
 
 	/* let's create and online css's */
 	kernfs_activate(kn);
@@ -5167,9 +5170,8 @@ int cgroup_rmdir(struct kernfs_node *kn)
 		return 0;
 
 	ret = cgroup_destroy_locked(cgrp);
-
 	if (!ret)
-		trace_cgroup_rmdir(cgrp);
+		TRACE_CGROUP_PATH(rmdir, cgrp);
 
 	cgroup_kn_unlock(kn);
 	return ret;