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 44066158f0d1..85bc9beb046d 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 2b4c20ab5bbe..29f815d2ef7e 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 13935886a471..fa178b62ea79 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