Revert "kernfs: remove kernfs_addrm_cxt"

This reverts commit 99177a34110889a8f2c36420c34e3bcc9bfd8a70.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 88 insertions, 26 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 770d687ee9f3..f878e4f2efe7 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -399,7 +399,28 @@ struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
 }
 
 /**
+ *      kernfs_addrm_start - prepare for kernfs_node add/remove
+ *      @acxt: pointer to kernfs_addrm_cxt to be used
+ *
+ *      This function is called when the caller is about to add or remove
+ *      kernfs_node.  This function acquires kernfs_mutex.  @acxt is used
+ *      to keep and pass context to other addrm functions.
+ *
+ *      LOCKING:
+ *      Kernel thread context (may sleep).  kernfs_mutex is locked on
+ *      return.
+ */
+void kernfs_addrm_start(struct kernfs_addrm_cxt *acxt)
+        __acquires(kernfs_mutex)
+{
+        memset(acxt, 0, sizeof(*acxt));
+
+        mutex_lock(&kernfs_mutex);
+}
+
+/**
  *      kernfs_add_one - add kernfs_node to parent without warning
+ *      @acxt: addrm context to use
  *      @kn: kernfs_node to be added
  *      @parent: the parent kernfs_node to add @kn to
  *
@@ -407,29 +428,34 @@ struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
  *      parent inode if @kn is a directory and link into the children list
  *      of the parent.
  *
+ *      This function should be called between calls to
+ *      kernfs_addrm_start() and kernfs_addrm_finish() and should be passed
+ *      the same @acxt as passed to kernfs_addrm_start().
+ *
+ *      LOCKING:
+ *      Determined by kernfs_addrm_start().
+ *
  *      RETURNS:
  *      0 on success, -EEXIST if entry with the given name already
  *      exists.
  */
-int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
+int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn,
+                  struct kernfs_node *parent)
 {
+        bool has_ns = kernfs_ns_enabled(parent);
         struct kernfs_iattrs *ps_iattr;
-        bool has_ns;
         int ret;
 
-        if (!kernfs_get_active(parent))
-                return -ENOENT;
+        WARN_ON_ONCE(atomic_read(&parent->active) < 0);
 
-        mutex_lock(&kernfs_mutex);
-
-        ret = -EINVAL;
-        has_ns = kernfs_ns_enabled(parent);
-        if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
-                 has_ns ? "required" : "invalid", parent->name, kn->name))
-                goto out_unlock;
+        if (has_ns != (bool)kn->ns) {
+                WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
+                     has_ns ? "required" : "invalid", parent->name, kn->name);
+                return -EINVAL;
+        }
 
         if (kernfs_type(parent) != KERNFS_DIR)
-                goto out_unlock;
+                return -EINVAL;
 
         kn->hash = kernfs_name_hash(kn->name, kn->ns);
         kn->parent = parent;
@@ -437,7 +463,7 @@ int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
 
         ret = kernfs_link_sibling(kn);
         if (ret)
-                goto out_unlock;
+                return ret;
 
         /* Update timestamps on the parent */
         ps_iattr = parent->iattr;
@@ -448,11 +474,34 @@ int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
 
         /* Mark the entry added into directory tree */
         atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
-        ret = 0;
-out_unlock:
+        return 0;
+}
+
+/**
+ *      kernfs_addrm_finish - finish up kernfs_node add/remove
+ *      @acxt: addrm context to finish up
+ *
+ *      Finish up kernfs_node add/remove.  Resources acquired by
+ *      kernfs_addrm_start() are released and removed kernfs_nodes are
+ *      cleaned up.
+ *
+ *      LOCKING:
+ *      kernfs_mutex is released.
+ */
+void kernfs_addrm_finish(struct kernfs_addrm_cxt *acxt)
+        __releases(kernfs_mutex)
+{
+        /* release resources acquired by kernfs_addrm_start() */
         mutex_unlock(&kernfs_mutex);
-        kernfs_put_active(parent);
-        return ret;
+
+        /* kill removed kernfs_nodes */
+        while (acxt->removed) {
+                struct kernfs_node *kn = acxt->removed;
+
+                acxt->removed = kn->u.removed_list;
+
+                kernfs_put(kn);
+        }
 }
 
 /**
@@ -584,6 +633,7 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
                                          const char *name, umode_t mode,
                                          void *priv, const void *ns)
 {
+        struct kernfs_addrm_cxt acxt;
         struct kernfs_node *kn;
         int rc;
 
@@ -598,7 +648,14 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
         kn->priv = priv;
 
         /* link in */
-        rc = kernfs_add_one(kn, parent);
+        rc = -ENOENT;
+        if (kernfs_get_active(parent)) {
+                kernfs_addrm_start(&acxt);
+                rc = kernfs_add_one(&acxt, kn, parent);
+                kernfs_addrm_finish(&acxt);
+                kernfs_put_active(parent);
+        }
+
         if (!rc)
                 return kn;
 
@@ -784,7 +841,8 @@ static void __kernfs_deactivate(struct kernfs_node *kn)
         }
 }
 
-static void __kernfs_remove(struct kernfs_node *kn)
+static void __kernfs_remove(struct kernfs_addrm_cxt *acxt,
+                            struct kernfs_node *kn)
 {
         struct kernfs_node *pos;
 
@@ -832,7 +890,8 @@ static void __kernfs_remove(struct kernfs_node *kn)
                                 ps_iattr->ia_iattr.ia_mtime = CURRENT_TIME;
                         }
 
-                        kernfs_put(pos);
+                        pos->u.removed_list = acxt->removed;
+                        acxt->removed = pos;
                 }
 
                 kernfs_put(pos);
@@ -847,9 +906,11 @@ static void __kernfs_remove(struct kernfs_node *kn)
  */
 void kernfs_remove(struct kernfs_node *kn)
 {
-        mutex_lock(&kernfs_mutex);
-        __kernfs_remove(kn);
-        mutex_unlock(&kernfs_mutex);
+        struct kernfs_addrm_cxt acxt;
+
+        kernfs_addrm_start(&acxt);
+        __kernfs_remove(&acxt, kn);
+        kernfs_addrm_finish(&acxt);
 }
 
 /**
@@ -864,6 +925,7 @@ void kernfs_remove(struct kernfs_node *kn)
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
                              const void *ns)
 {
+        struct kernfs_addrm_cxt acxt;
         struct kernfs_node *kn;
 
         if (!parent) {
@@ -872,13 +934,13 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
                 return -ENOENT;
         }
 
-        mutex_lock(&kernfs_mutex);
+        kernfs_addrm_start(&acxt);
 
         kn = kernfs_find_ns(parent, name, ns);
         if (kn)
-                __kernfs_remove(kn);
+                __kernfs_remove(&acxt, kn);
 
-        mutex_unlock(&kernfs_mutex);
+        kernfs_addrm_finish(&acxt);
 
         if (kn)
                 return 0;