Btrfs: tree mod log's old roots could still be part of the tree

Tree mod log treated old root buffers as always empty buffers when starting
the rewind operations. However, the old root may still be part of the
current tree at a lower level, with still some valid entries.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 21 insertions, 4 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index e6b75ccd2850..d9308c38a8f2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1239,6 +1239,7 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
         struct tree_mod_root *old_root = NULL;
         u64 old_generation = 0;
         u64 logical;
+        u32 blocksize;
 
         eb = btrfs_read_lock_root_node(root);
         tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
@@ -1254,12 +1255,28 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
         }
 
         tm = tree_mod_log_search(root->fs_info, logical, time_seq);
-        if (old_root)
+        if (old_root && tm && tm->op != MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
+                btrfs_tree_read_unlock(root->node);
+                free_extent_buffer(root->node);
+                blocksize = btrfs_level_size(root, old_root->level);
+                eb = read_tree_block(root, logical, blocksize, 0);
+                if (!eb) {
+                        pr_warn("btrfs: failed to read tree block %llu from get_old_root\n",
+                                logical);
+                        WARN_ON(1);
+                } else {
+                        eb = btrfs_clone_extent_buffer(eb);
+                }
+        } else if (old_root) {
+                btrfs_tree_read_unlock(root->node);
+                free_extent_buffer(root->node);
                 eb = alloc_dummy_extent_buffer(logical, root->nodesize);
-        else
+        } else {
                 eb = btrfs_clone_extent_buffer(root->node);
-        btrfs_tree_read_unlock(root->node);
-        free_extent_buffer(root->node);
+                btrfs_tree_read_unlock(root->node);
+                free_extent_buffer(root->node);
+        }
+
         if (!eb)
                 return NULL;
         btrfs_tree_read_lock(eb);