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()

block/blk-cgroup.c

@@ -1340,10 +1340,8 @@ int blkcg_policy_register(struct blkcg_policy *pol)
 			struct blkcg_policy_data *cpd;
 
 			cpd = pol->cpd_alloc_fn(GFP_KERNEL);
-			if (!cpd) {
-				mutex_unlock(&blkcg_pol_mutex);
+			if (!cpd)
 				goto err_free_cpds;
-			}
 
 			blkcg->cpd[pol->plid] = cpd;
 			cpd->blkcg = blkcg;

fs/kernfs/dir.c

@@ -110,8 +110,9 @@ static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
  * kn_to:   /n1/n2/n3         [depth=3]
  * result:  /../..
  *
- * return value: length of the string.  If greater than buflen,
- * then contents of buf are undefined.  On error, -1 is returned.
+ * Returns the length of the full path.  If the full length is equal to or
+ * greater than @buflen, @buf contains the truncated path with the trailing
+ * '\0'.  On error, -errno is returned.
  */
 static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 					struct kernfs_node *kn_from,
@@ -119,9 +120,8 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 {
 	struct kernfs_node *kn, *common;
 	const char parent_str[] = "/..";
-	size_t depth_from, depth_to, len = 0, nlen = 0;
-	char *p;
-	int i;
+	size_t depth_from, depth_to, len = 0;
+	int i, j;
 
 	if (!kn_from)
 		kn_from = kernfs_root(kn_to)->kn;
@@ -131,7 +131,7 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 
 	common = kernfs_common_ancestor(kn_from, kn_to);
 	if (WARN_ON(!common))
-		return -1;
+		return -EINVAL;
 
 	depth_to = kernfs_depth(common, kn_to);
 	depth_from = kernfs_depth(common, kn_from);
@@ -144,22 +144,16 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 			       len < buflen ? buflen - len : 0);
 
 	/* Calculate how many bytes we need for the rest */
-	for (kn = kn_to; kn != common; kn = kn->parent)
-		nlen += strlen(kn->name) + 1;
-
-	if (len + nlen >= buflen)
-		return len + nlen;
-
-	p = buf + len + nlen;
-	*p = '\0';
-	for (kn = kn_to; kn != common; kn = kn->parent) {
-		size_t tmp = strlen(kn->name);
-		p -= tmp;
-		memcpy(p, kn->name, tmp);
-		*(--p) = '/';
+	for (i = depth_to - 1; i >= 0; i--) {
+		for (kn = kn_to, j = 0; j < i; j++)
+			kn = kn->parent;
+		len += strlcpy(buf + len, "/",
+			       len < buflen ? buflen - len : 0);
+		len += strlcpy(buf + len, kn->name,
+			       len < buflen ? buflen - len : 0);
 	}
 
-	return len + nlen;
+	return len;
 }
 
 /**
@@ -185,29 +179,6 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 	return ret;
 }
 
-/**
- * kernfs_path_len - determine the length of the full path of a given node
- * @kn: kernfs_node of interest
- *
- * The returned length doesn't include the space for the terminating '\0'.
- */
-size_t kernfs_path_len(struct kernfs_node *kn)
-{
-	size_t len = 0;
-	unsigned long flags;
-
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
-
-	do {
-		len += strlen(kn->name) + 1;
-		kn = kn->parent;
-	} while (kn && kn->parent);
-
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
-
-	return len;
-}
-
 /**
  * kernfs_path_from_node - build path of node @to relative to @from.
  * @from: parent kernfs_node relative to which we need to build the path
@@ -220,8 +191,9 @@ size_t kernfs_path_len(struct kernfs_node *kn)
  * path (which includes '..'s) as needed to reach from @from to @to is
  * returned.
  *
- * If @buf isn't long enough, the return value will be greater than @buflen
- * and @buf contents are undefined.
+ * Returns the length of the full path.  If the full length is equal to or
+ * greater than @buflen, @buf contains the truncated path with the trailing
+ * '\0'.  On error, -errno is returned.
  */
 int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
 			  char *buf, size_t buflen)
@@ -236,28 +208,6 @@ int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
 }
 EXPORT_SYMBOL_GPL(kernfs_path_from_node);
 
-/**
- * kernfs_path - build full path of a given node
- * @kn: kernfs_node of interest
- * @buf: buffer to copy @kn's name into
- * @buflen: size of @buf
- *
- * Builds and returns the full path of @kn in @buf of @buflen bytes.  The
- * path is built from the end of @buf so the returned pointer usually
- * doesn't match @buf.  If @buf isn't long enough, @buf is nul terminated
- * and %NULL is returned.
- */
-char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
-{
-	int ret;
-
-	ret = kernfs_path_from_node(kn, NULL, buf, buflen);
-	if (ret < 0 || ret >= buflen)
-		return NULL;
-	return buf;
-}
-EXPORT_SYMBOL_GPL(kernfs_path);
-
 /**
  * pr_cont_kernfs_name - pr_cont name of a kernfs_node
  * @kn: kernfs_node of interest

fs/sysfs/dir.c

@@ -21,14 +21,14 @@ DEFINE_SPINLOCK(sysfs_symlink_target_lock);
 
 void sysfs_warn_dup(struct kernfs_node *parent, const char *name)
 {
-	char *buf, *path = NULL;
+	char *buf;
 
 	buf = kzalloc(PATH_MAX, GFP_KERNEL);
 	if (buf)
-		path = kernfs_path(parent, buf, PATH_MAX);
+		kernfs_path(parent, buf, PATH_MAX);
 
 	WARN(1, KERN_WARNING "sysfs: cannot create duplicate filename '%s/%s'\n",
-	     path, name);
+	     buf, name);
 
 	kfree(buf);
 }

include/linux/blk-cgroup.h

@@ -343,16 +343,7 @@ static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
  */
 static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
 {
-	char *p;
-
-	p = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
-	if (!p) {
-		strncpy(buf, "<unavailable>", buflen);
-		return -ENAMETOOLONG;
-	}
-
-	memmove(buf, p, buf + buflen - p);
-	return 0;
+	return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
 }
 
 /**

include/linux/cgroup.h

@@ -97,7 +97,7 @@ int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 void cgroup_file_notify(struct cgroup_file *cfile);
 
-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);
 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		     struct pid *pid, struct task_struct *tsk);
@@ -555,8 +555,7 @@ static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
 	return kernfs_name(cgrp->kn, buf, buflen);
 }
 
-static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
-					      size_t buflen)
+static inline int cgroup_path(struct cgroup *cgrp, char *buf, size_t buflen)
 {
 	return kernfs_path(cgrp->kn, buf, buflen);
 }
@@ -658,8 +657,8 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
 					struct user_namespace *user_ns,
 					struct cgroup_namespace *old_ns);
 
-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);
 
 #else /* !CONFIG_CGROUPS */
 

include/linux/kernfs.h

@@ -269,10 +269,8 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 }
 
 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
-size_t kernfs_path_len(struct kernfs_node *kn);
 int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
 			  char *buf, size_t buflen);
-char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen);
 void pr_cont_kernfs_name(struct kernfs_node *kn);
 void pr_cont_kernfs_path(struct kernfs_node *kn);
 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
@@ -341,12 +339,10 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 { return -ENOSYS; }
 
-static inline size_t kernfs_path_len(struct kernfs_node *kn)
-{ return 0; }
-
-static inline char *kernfs_path(struct kernfs_node *kn, char *buf,
-				size_t buflen)
-{ return NULL; }
+static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
+					struct kernfs_node *kn,
+					char *buf, size_t buflen)
+{ return -ENOSYS; }
 
 static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
 static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }
@@ -436,6 +432,22 @@ static inline void kernfs_init(void) { }
 
 #endif	/* CONFIG_KERNFS */
 
+/**
+ * kernfs_path - build full path of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Builds and returns the full path of @kn in @buf of @buflen bytes.  The
+ * path is built from the end of @buf so the returned pointer usually
+ * doesn't match @buf.  If @buf isn't long enough, @buf is nul terminated
+ * and %NULL is returned.
+ */
+static inline int kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	return kernfs_path_from_node(kn, NULL, buf, buflen);
+}
+
 static inline struct kernfs_node *
 kernfs_find_and_get(struct kernfs_node *kn, const char *name)
 {

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>

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 */

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:

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