1 files changed, 29 insertions, 10 deletions

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 8c41b52da358..1e3b99d3db0d 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -66,7 +66,7 @@ static struct inode *debugfs_get_inode(struct super_block *sb, umode_t mode, dev
 			break;
 		}
 	}
-	return inode; 
+	return inode;
 }
 
 /* SMP-safe */
@@ -317,7 +317,7 @@ static struct dentry *__create_file(const char *name, umode_t mode,
 		goto exit;
 
 	/* If the parent is not specified, we create it in the root.
-	 * We need the root dentry to do this, which is in the super 
+	 * We need the root dentry to do this, which is in the super
 	 * block. A pointer to that is in the struct vfsmount that we
 	 * have around.
 	 */
@@ -330,7 +330,7 @@ static struct dentry *__create_file(const char *name, umode_t mode,
 		switch (mode & S_IFMT) {
 		case S_IFDIR:
 			error = debugfs_mkdir(parent->d_inode, dentry, mode);
-					      
+
 			break;
 		case S_IFLNK:
 			error = debugfs_link(parent->d_inode, dentry, mode,
@@ -534,7 +534,7 @@ EXPORT_SYMBOL_GPL(debugfs_remove);
  */
 void debugfs_remove_recursive(struct dentry *dentry)
 {
-	struct dentry *child, *next, *parent;
+	struct dentry *child, *parent;
 
 	if (IS_ERR_OR_NULL(dentry))
 		return;
@@ -546,30 +546,49 @@ void debugfs_remove_recursive(struct dentry *dentry)
 	parent = dentry;
  down:
 	mutex_lock(&parent->d_inode->i_mutex);
-	list_for_each_entry_safe(child, next, &parent->d_subdirs, d_u.d_child) {
+ loop:
+	/*
+	 * The parent->d_subdirs is protected by the d_lock. Outside that
+	 * lock, the child can be unlinked and set to be freed which can
+	 * use the d_u.d_child as the rcu head and corrupt this list.
+	 */
+	spin_lock(&parent->d_lock);
+	list_for_each_entry(child, &parent->d_subdirs, d_u.d_child) {
 		if (!debugfs_positive(child))
 			continue;
 
 		/* perhaps simple_empty(child) makes more sense */
 		if (!list_empty(&child->d_subdirs)) {
+			spin_unlock(&parent->d_lock);
 			mutex_unlock(&parent->d_inode->i_mutex);
 			parent = child;
 			goto down;
 		}
- up:
+
+		spin_unlock(&parent->d_lock);
+
 		if (!__debugfs_remove(child, parent))
 			simple_release_fs(&debugfs_mount, &debugfs_mount_count);
+
+		/*
+		 * The parent->d_lock protects agaist child from unlinking
+		 * from d_subdirs. When releasing the parent->d_lock we can
+		 * no longer trust that the next pointer is valid.
+		 * Restart the loop. We'll skip this one with the
+		 * debugfs_positive() check.
+		 */
+		goto loop;
 	}
+	spin_unlock(&parent->d_lock);
 
 	mutex_unlock(&parent->d_inode->i_mutex);
 	child = parent;
 	parent = parent->d_parent;
 	mutex_lock(&parent->d_inode->i_mutex);
 
-	if (child != dentry) {
-		next = list_next_entry(child, d_u.d_child);
-		goto up;
-	}
+	if (child != dentry)
+		/* go up */
+		goto loop;
 
 	if (!__debugfs_remove(child, parent))
 		simple_release_fs(&debugfs_mount, &debugfs_mount_count);