[PATCH 3.16 49/63] btrfs: relocation: Only remove reloc rb_trees if reloc control has been initialized

[Ben Hutchings]

3.16.58-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Qu Wenruo <wqu@xxxxxxxx>

commit 389305b2aa68723c754f88d9dbd268a400e10664 upstream.

Invalid reloc tree can cause kernel NULL pointer dereference when btrfs
does some cleanup of the reloc roots.

It turns out that fs_info::reloc_ctl can be NULL in
btrfs_recover_relocation() as we allocate relocation control after all
reloc roots have been verified.
So when we hit: note, we haven't called set_reloc_control() thus
fs_info::reloc_ctl is still NULL.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199833
Reported-by: Xu Wen <wen.xu@xxxxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Tested-by: Gu Jinxiang <gujx@xxxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/btrfs/relocation.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1311,18 +1311,19 @@ static void __del_reloc_root(struct btrf
 	struct mapping_node *node = NULL;
 	struct reloc_control *rc = root->fs_info->reloc_ctl;
 
-	spin_lock(&rc->reloc_root_tree.lock);
-	rb_node = tree_search(&rc->reloc_root_tree.rb_root,
-			      root->node->start);
-	if (rb_node) {
-		node = rb_entry(rb_node, struct mapping_node, rb_node);
-		rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
+	if (rc) {
+		spin_lock(&rc->reloc_root_tree.lock);
+		rb_node = tree_search(&rc->reloc_root_tree.rb_root,
+				      root->node->start);
+		if (rb_node) {
+			node = rb_entry(rb_node, struct mapping_node, rb_node);
+			rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
+		}
+		spin_unlock(&rc->reloc_root_tree.lock);
+		if (!node)
+			return;
+		BUG_ON((struct btrfs_root *)node->data != root);
 	}
-	spin_unlock(&rc->reloc_root_tree.lock);
-
-	if (!node)
-		return;
-	BUG_ON((struct btrfs_root *)node->data != root);
 
 	spin_lock(&root->fs_info->trans_lock);
 	list_del_init(&root->root_list);