Merge branch 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - tracepoints for basic cgroup management operations added

 - kernfs and cgroup path formatting functions updated to behave in the
   style of strlcpy()

 - non-critical bug fixes

* 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  blkcg: Unlock blkcg_pol_mutex only once when cpd == NULL
  cgroup: fix error handling regressions in proc_cgroup_show() and cgroup_release_agent()
  cpuset: fix error handling regression in proc_cpuset_show()
  cgroup: add tracepoints for basic operations
  cgroup: make cgroup_path() and friends behave in the style of strlcpy()
  kernfs: remove kernfs_path_len()
  kernfs: make kernfs_path*() behave in the style of strlcpy()
  kernfs: add dummy implementation of kernfs_path_from_node()

3 files changed, 57 insertions, 34 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 44066158f0d1f..85bc9beb046d9 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
@@ -2315,22 +2325,18 @@ static struct file_system_type cgroup2_fs_type = {
 	.fs_flags = FS_USERNS_MOUNT,
 };
 
-static char *cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
-				   struct cgroup_namespace *ns)
+static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
+				 struct cgroup_namespace *ns)
 {
 	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
-	int ret;
 
-	ret = kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
-	if (ret < 0 || ret >= buflen)
-		return NULL;
-	return buf;
+	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
 }
 
-char *cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
-		     struct cgroup_namespace *ns)
+int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
+		   struct cgroup_namespace *ns)
 {
-	char *ret;
+	int ret;
 
 	mutex_lock(&cgroup_mutex);
 	spin_lock_irq(&css_set_lock);
@@ -2357,12 +2363,12 @@ EXPORT_SYMBOL_GPL(cgroup_path_ns);
  *
  * Return value is the same as kernfs_path().
  */
-char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 {
 	struct cgroup_root *root;
 	struct cgroup *cgrp;
 	int hierarchy_id = 1;
-	char *path = NULL;
+	int ret;
 
 	mutex_lock(&cgroup_mutex);
 	spin_lock_irq(&css_set_lock);
@@ -2371,16 +2377,15 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 
 	if (root) {
 		cgrp = task_cgroup_from_root(task, root);
-		path = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
+		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
 	} else {
 		/* if no hierarchy exists, everyone is in "/" */
-		if (strlcpy(buf, "/", buflen) < buflen)
-			path = buf;
+		ret = strlcpy(buf, "/", buflen);
 	}
 
 	spin_unlock_irq(&css_set_lock);
 	mutex_unlock(&cgroup_mutex);
-	return path;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(task_cgroup_path);
 
@@ -2830,6 +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;
 }
 
@@ -3611,6 +3620,8 @@ 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);
 
@@ -4381,6 +4392,8 @@ 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);
@@ -5046,6 +5059,8 @@ 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;
 
@@ -5332,6 +5347,8 @@ 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);
 
@@ -5507,6 +5524,9 @@ 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;
 }
@@ -5743,7 +5763,7 @@ core_initcall(cgroup_wq_init);
 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		     struct pid *pid, struct task_struct *tsk)
 {
-	char *buf, *path;
+	char *buf;
 	int retval;
 	struct cgroup_root *root;
 
@@ -5786,18 +5806,18 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		 * " (deleted)" is appended to the cgroup path.
 		 */
 		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
-			path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
+			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
 						current->nsproxy->cgroup_ns);
-			if (!path) {
+			if (retval >= PATH_MAX)
 				retval = -ENAMETOOLONG;
+			if (retval < 0)
 				goto out_unlock;
-			}
+
+			seq_puts(m, buf);
 		} else {
-			path = "/";
+			seq_puts(m, "/");
 		}
 
-		seq_puts(m, path);
-
 		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
 			seq_puts(m, " (deleted)\n");
 		else
@@ -6062,8 +6082,9 @@ static void cgroup_release_agent(struct work_struct *work)
 {
 	struct cgroup *cgrp =
 		container_of(work, struct cgroup, release_agent_work);
-	char *pathbuf = NULL, *agentbuf = NULL, *path;
+	char *pathbuf = NULL, *agentbuf = NULL;
 	char *argv[3], *envp[3];
+	int ret;
 
 	mutex_lock(&cgroup_mutex);
 
@@ -6073,13 +6094,13 @@ static void cgroup_release_agent(struct work_struct *work)
 		goto out;
 
 	spin_lock_irq(&css_set_lock);
-	path = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
+	ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
 	spin_unlock_irq(&css_set_lock);
-	if (!path)
+	if (ret < 0 || ret >= PATH_MAX)
 		goto out;
 
 	argv[0] = agentbuf;
-	argv[1] = path;
+	argv[1] = pathbuf;
 	argv[2] = NULL;
 
 	/* minimal command environment */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 2b4c20ab5bbe1..29f815d2ef7e3 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2715,7 +2715,7 @@ void __cpuset_memory_pressure_bump(void)
 int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
 		     struct pid *pid, struct task_struct *tsk)
 {
-	char *buf, *p;
+	char *buf;
 	struct cgroup_subsys_state *css;
 	int retval;
 
@@ -2724,14 +2724,15 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
 	if (!buf)
 		goto out;
 
-	retval = -ENAMETOOLONG;
 	css = task_get_css(tsk, cpuset_cgrp_id);
-	p = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
-			   current->nsproxy->cgroup_ns);
+	retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
+				current->nsproxy->cgroup_ns);
 	css_put(css);
-	if (!p)
+	if (retval >= PATH_MAX)
+		retval = -ENAMETOOLONG;
+	if (retval < 0)
 		goto out_free;
-	seq_puts(m, p);
+	seq_puts(m, buf);
 	seq_putc(m, '\n');
 	retval = 0;
 out_free:
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 13935886a4711..fa178b62ea79b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -415,7 +415,8 @@ static char *task_group_path(struct task_group *tg)
 	if (autogroup_path(tg, group_path, PATH_MAX))
 		return group_path;
 
-	return cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
+	cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
+	return group_path;
 }
 #endif