[PATCH v4 05/10] eventfs: Implement eventfs file, directory remove function

[Ajay Kaher]

Adding eventfs_remove(), this function will recursively remove
dir or file info from eventfs.

added a recursion check to eventfs_remove_rec() as it is really
dangerous to have unchecked recursion in the kernel (we do have
a fixed size stack).

have the free use srcu callbacks. After the srcu grace periods
are done, it adds the eventfs_file onto a llist (lockless link
list) and wakes up a work queue. Then the work queue does the
freeing (this needs to be done in task/workqueue context, as
srcu callbacks are done in softirq context).

Signed-off-by: Ajay Kaher <akaher@xxxxxxxxxx>
Co-developed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Tested-by: Ching-lin Yu <chinglinyu@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202305030611.Kas747Ev-lkp@xxxxxxxxx/
---
 fs/tracefs/event_inode.c | 110 +++++++++++++++++++++++++++++++++++++++
 include/linux/tracefs.h  |   4 ++
 2 files changed, 114 insertions(+)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 75dc8953d813..322a77be5a56 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -45,6 +45,7 @@ struct eventfs_file {
 };
 
 static DEFINE_MUTEX(eventfs_mutex);
+DEFINE_STATIC_SRCU(eventfs_srcu);
 
 static const struct file_operations eventfs_file_operations = {
 };
@@ -299,3 +300,112 @@ int eventfs_add_file(const char *name, umode_t mode,
 	mutex_unlock(&eventfs_mutex);
 	return 0;
 }
+
+static LLIST_HEAD(free_list);
+
+static void eventfs_workfn(struct work_struct *work)
+{
+	struct eventfs_file *ef, *tmp;
+	struct llist_node *llnode;
+
+	llnode = llist_del_all(&free_list);
+	llist_for_each_entry_safe(ef, tmp, llnode, llist) {
+		if (ef->created && ef->dentry)
+			dput(ef->dentry);
+		kfree(ef->name);
+		kfree(ef->ei);
+		kfree(ef);
+	}
+}
+
+DECLARE_WORK(eventfs_work, eventfs_workfn);
+
+static void free_ef(struct rcu_head *head)
+{
+	struct eventfs_file *ef = container_of(head, struct eventfs_file, rcu);
+
+	if (!llist_add(&ef->llist, &free_list))
+		return;
+
+	queue_work(system_unbound_wq, &eventfs_work);
+}
+
+
+
+/**
+ * eventfs_remove_rec - remove eventfs dir or file from list
+ * @ef: eventfs_file to be removed.
+ *
+ * This function recursively remove eventfs_file which
+ * contains info of file or dir.
+ */
+static void eventfs_remove_rec(struct eventfs_file *ef, int level)
+{
+	struct eventfs_file *ef_child;
+
+	if (!ef)
+		return;
+	/*
+	 * Check recursion depth. It should never be greater than 3:
+	 * 0 - events/
+	 * 1 - events/group/
+	 * 2 - events/group/event/
+	 * 3 - events/group/event/file
+	 */
+	if (WARN_ON_ONCE(level > 3))
+		return;
+
+	if (ef->ei) {
+		/* search for nested folders or files */
+		list_for_each_entry_srcu(ef_child, &ef->ei->e_top_files, list,
+					 lockdep_is_held(&eventfs_mutex)) {
+			eventfs_remove_rec(ef_child, level + 1);
+		}
+	}
+
+	if (ef->created && ef->dentry)
+		d_invalidate(ef->dentry);
+
+	list_del_rcu(&ef->list);
+	call_srcu(&eventfs_srcu, &ef->rcu, free_ef);
+}
+
+/**
+ * eventfs_remove - remove eventfs dir or file from list
+ * @ef: eventfs_file to be removed.
+ *
+ * This function acquire the eventfs_mutex lock and call eventfs_remove_rec()
+ */
+void eventfs_remove(struct eventfs_file *ef)
+{
+	if (!ef)
+		return;
+
+	mutex_lock(&eventfs_mutex);
+	eventfs_remove_rec(ef, 0);
+	mutex_unlock(&eventfs_mutex);
+}
+
+/**
+ * eventfs_remove_events_dir - remove eventfs dir or file from list
+ * @dentry: events's dentry to be removed.
+ *
+ * This function remove events main directory
+ */
+void eventfs_remove_events_dir(struct dentry *dentry)
+{
+	struct tracefs_inode *ti;
+	struct eventfs_inode *ei;
+
+	if (!dentry || !dentry->d_inode)
+		return;
+
+	ti = get_tracefs(dentry->d_inode);
+	if (!ti || !(ti->flags & TRACEFS_EVENT_INODE))
+		return;
+
+	ei = ti->private;
+	d_invalidate(dentry);
+	dput(dentry);
+	kfree(ei);
+}
diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
index a51312ff803c..2c08edd4a739 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h
@@ -40,6 +40,10 @@ int eventfs_add_top_file(const char *name, umode_t mode,
 			 struct dentry *parent, void *data,
 			 const struct file_operations *fops);
 
+void eventfs_remove(struct eventfs_file *ef);
+
+void eventfs_remove_events_dir(struct dentry *dentry);
+
 struct dentry *tracefs_create_file(const char *name, umode_t mode,
 				   struct dentry *parent, void *data,
 				   const struct file_operations *fops);
-- 
2.39.0