3 files changed, 35 insertions, 25 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 60d44b26276d..869fd4a3d28e 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -90,7 +90,6 @@ enum {
  */
 struct cgroup_file {
         /* do not access any fields from outside cgroup core */
-        struct list_head node;                  /* anchored at css->files */
         struct kernfs_node *kn;
 };
 
@@ -134,9 +133,6 @@ struct cgroup_subsys_state {
          */
         u64 serial_nr;
 
-        /* all cgroup_files associated with this css */
-        struct list_head files;
-
         /* percpu_ref killing and RCU release */
         struct rcu_head rcu_head;
         struct work_struct destroy_work;
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 22e3754f89c5..f64083030ad5 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -88,6 +88,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 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 cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
@@ -516,19 +517,6 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
         pr_cont_kernfs_path(cgrp->kn);
 }
 
-/**
- * cgroup_file_notify - generate a file modified event for a cgroup_file
- * @cfile: target cgroup_file
- *
- * @cfile must have been obtained by setting cftype->file_offset.
- */
-static inline void cgroup_file_notify(struct cgroup_file *cfile)
-{
-        /* might not have been created due to one of the CFTYPE selector flags */
-        if (cfile->kn)
-                kernfs_notify(cfile->kn);
-}
-
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f1603c153890..b316debadeb3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -98,6 +98,12 @@ static DEFINE_SPINLOCK(css_set_lock);
 static DEFINE_SPINLOCK(cgroup_idr_lock);
 
 /*
+ * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
+ * against file removal/re-creation across css hiding.
+ */
+static DEFINE_SPINLOCK(cgroup_file_kn_lock);
+
+/*
  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
  */
@@ -1393,6 +1399,16 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
         char name[CGROUP_FILE_NAME_MAX];
 
         lockdep_assert_held(&cgroup_mutex);
+
+        if (cft->file_offset) {
+                struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
+                struct cgroup_file *cfile = (void *)css + cft->file_offset;
+
+                spin_lock_irq(&cgroup_file_kn_lock);
+                cfile->kn = NULL;
+                spin_unlock_irq(&cgroup_file_kn_lock);
+        }
+
         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
 }
 
@@ -1856,7 +1872,6 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
 
         INIT_LIST_HEAD(&cgrp->self.sibling);
         INIT_LIST_HEAD(&cgrp->self.children);
-        INIT_LIST_HEAD(&cgrp->self.files);
         INIT_LIST_HEAD(&cgrp->cset_links);
         INIT_LIST_HEAD(&cgrp->pidlists);
         mutex_init(&cgrp->pidlist_mutex);
@@ -3313,9 +3328,9 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
         if (cft->file_offset) {
                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
 
-                kernfs_get(kn);
+                spin_lock_irq(&cgroup_file_kn_lock);
                 cfile->kn = kn;
-                list_add(&cfile->node, &css->files);
+                spin_unlock_irq(&cgroup_file_kn_lock);
         }
 
         return 0;
@@ -3553,6 +3568,22 @@ int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 }
 
 /**
+ * cgroup_file_notify - generate a file modified event for a cgroup_file
+ * @cfile: target cgroup_file
+ *
+ * @cfile must have been obtained by setting cftype->file_offset.
+ */
+void cgroup_file_notify(struct cgroup_file *cfile)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&cgroup_file_kn_lock, flags);
+        if (cfile->kn)
+                kernfs_notify(cfile->kn);
+        spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
+}
+
+/**
  * cgroup_task_count - count the number of tasks in a cgroup.
  * @cgrp: the cgroup in question
  *
@@ -4613,13 +4644,9 @@ static void css_free_work_fn(struct work_struct *work)
                 container_of(work, struct cgroup_subsys_state, destroy_work);
         struct cgroup_subsys *ss = css->ss;
         struct cgroup *cgrp = css->cgroup;
-        struct cgroup_file *cfile;
 
         percpu_ref_exit(&css->refcnt);
 
-        list_for_each_entry(cfile, &css->files, node)
-                kernfs_put(cfile->kn);
-
         if (ss) {
                 /* css free path */
                 int id = css->id;
@@ -4724,7 +4751,6 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
         css->ss = ss;
         INIT_LIST_HEAD(&css->sibling);
         INIT_LIST_HEAD(&css->children);
-        INIT_LIST_HEAD(&css->files);
         css->serial_nr = css_serial_nr_next++;
 
         if (cgroup_parent(cgrp)) {