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

3 files changed, 35 insertions, 7 deletions

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;