2 files changed, 85 insertions, 14 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index e3d37f607f97..d895b4b7b661 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -39,6 +39,19 @@ struct kernfs_open_node {
         struct list_head        files; /* goes through kernfs_open_file.list */
 };
 
+/*
+ * kernfs_notify() may be called from any context and bounces notifications
+ * through a work item.  To minimize space overhead in kernfs_node, the
+ * pending queue is implemented as a singly linked list of kernfs_nodes.
+ * The list is terminated with the self pointer so that whether a
+ * kernfs_node is on the list or not can be determined by testing the next
+ * pointer for NULL.
+ */
+#define KERNFS_NOTIFY_EOL                       ((void *)&kernfs_notify_list)
+
+static DEFINE_SPINLOCK(kernfs_notify_lock);
+static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
+
 static struct kernfs_open_file *kernfs_of(struct file *file)
 {
         return ((struct seq_file *)file->private_data)->private;
@@ -783,24 +796,25 @@ static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
         return DEFAULT_POLLMASK|POLLERR|POLLPRI;
 }
 
-/**
- * kernfs_notify - notify a kernfs file
- * @kn: file to notify
- *
- * Notify @kn such that poll(2) on @kn wakes up.
- */
-void kernfs_notify(struct kernfs_node *kn)
+static void kernfs_notify_workfn(struct work_struct *work)
 {
-        struct kernfs_root *root = kernfs_root(kn);
+        struct kernfs_node *kn;
         struct kernfs_open_node *on;
         struct kernfs_super_info *info;
-        unsigned long flags;
-
-        if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
+repeat:
+        /* pop one off the notify_list */
+        spin_lock_irq(&kernfs_notify_lock);
+        kn = kernfs_notify_list;
+        if (kn == KERNFS_NOTIFY_EOL) {
+                spin_unlock_irq(&kernfs_notify_lock);
                 return;
+        }
+        kernfs_notify_list = kn->attr.notify_next;
+        kn->attr.notify_next = NULL;
+        spin_unlock_irq(&kernfs_notify_lock);
 
         /* kick poll */
-        spin_lock_irqsave(&kernfs_open_node_lock, flags);
+        spin_lock_irq(&kernfs_open_node_lock);
 
         on = kn->attr.open;
         if (on) {
@@ -808,12 +822,12 @@ void kernfs_notify(struct kernfs_node *kn)
                 wake_up_interruptible(&on->poll);
         }
 
-        spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+        spin_unlock_irq(&kernfs_open_node_lock);
 
         /* kick fsnotify */
         mutex_lock(&kernfs_mutex);
 
-        list_for_each_entry(info, &root->supers, node) {
+        list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
                 struct inode *inode;
                 struct dentry *dentry;
 
@@ -833,6 +847,33 @@ void kernfs_notify(struct kernfs_node *kn)
         }
 
         mutex_unlock(&kernfs_mutex);
+        kernfs_put(kn);
+        goto repeat;
+}
+
+/**
+ * kernfs_notify - notify a kernfs file
+ * @kn: file to notify
+ *
+ * Notify @kn such that poll(2) on @kn wakes up.  Maybe be called from any
+ * context.
+ */
+void kernfs_notify(struct kernfs_node *kn)
+{
+        static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
+        unsigned long flags;
+
+        if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
+                return;
+
+        spin_lock_irqsave(&kernfs_notify_lock, flags);
+        if (!kn->attr.notify_next) {
+                kernfs_get(kn);
+                kn->attr.notify_next = kernfs_notify_list;
+                kernfs_notify_list = kn;
+                schedule_work(&kernfs_notify_work);
+        }
+        spin_unlock_irqrestore(&kernfs_notify_lock, flags);
 }
 EXPORT_SYMBOL_GPL(kernfs_notify);
 
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index d171b98a6cdd..f973ae9b05f1 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -211,6 +211,36 @@ void kernfs_kill_sb(struct super_block *sb)
         kernfs_put(root_kn);
 }
 
+/**
+ * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
+ * @kernfs_root: the kernfs_root in question
+ * @ns: the namespace tag
+ *
+ * Pin the superblock so the superblock won't be destroyed in subsequent
+ * operations.  This can be used to block ->kill_sb() which may be useful
+ * for kernfs users which dynamically manage superblocks.
+ *
+ * Returns NULL if there's no superblock associated to this kernfs_root, or
+ * -EINVAL if the superblock is being freed.
+ */
+struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
+{
+        struct kernfs_super_info *info;
+        struct super_block *sb = NULL;
+
+        mutex_lock(&kernfs_mutex);
+        list_for_each_entry(info, &root->supers, node) {
+                if (info->ns == ns) {
+                        sb = info->sb;
+                        if (!atomic_inc_not_zero(&info->sb->s_active))
+                                sb = ERR_PTR(-EINVAL);
+                        break;
+                }
+        }
+        mutex_unlock(&kernfs_mutex);
+        return sb;
+}
+
 void __init kernfs_init(void)
 {
         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",